PART III.

THE BLOOD, LYMPH, AND HISTOLOGY OF THE VESSELS.

[The parts described in this section will be considered very briefly, and only from an anatomical point of view.

A. The *blood*[65].

[Footnote 65: Mr. Hurst has noticed a frog (R. temporaria) in which the blood was perfectly colourless.]

The blood varies in colour, according as it is obtained from an artery or from a vein; from an artery it has a bright red or scarlet colour; from a vein a darker shade: in the pulmonary vessels these colours are reversed. The blood consists of a fluid plasma which contains red and white corpuscles: the whole forming a slightly alkaline, opaque, and somewhat sticky fluid.

*a.* The *plasma* or _liquor sanguinis_ is a transparent, clear, slightly yellow fluid, faintly alkaline in reaction.

*b.* The *corpuscles* are of two kinds, colourless and coloured.

(1) The colourless or white corpuscles are subspherical masses of protoplasm, endowed with the power of spontaneous motion. They are much fewer than the red corpuscles, though the proportion of white to red varies considerably. Three chief varieties of colourless corpuscles can be distinguished, all of which are true cell forms, and behave like other cells with staining or other reagents. They have no cell-wall, but are simply nucleated masses of protoplasm. These corpuscles possess the power of passing through the walls of the blood-vessels, and are then known as migratory cells; such migratory cells can be found in nearly all tissues, but more especially in the connective-tissues.

α. Ordinary large colourless corpuscles are large transparent masses of protoplasm containing one or two nuclei, rarely three or more. The cell contains few granules, and usually has one or more vacuoles or clear spaces containing fluid.

β. Granular corpuscles are less numerous than the foregoing, but larger, and are distinguished by the numerous large dark granules which they contain. The processes such a corpuscle sends out are hyaline.

γ. Smaller corpuscles also occur varying much in form: they may consist of a nucleus with a very small amount of hyaline or granular protoplasm, or of several nuclei with an extremely small amount of protoplasm.

(2) The *coloured corpuscles* are much more numerous than the colourless corpuscles; each is a bi-concave, oval disc, about 0.0255 mm. in length, and 0.017 mm in breadth (Gulliver)[66] (R. temporaria, 0.0235 and 0.0145 mm. respectively). Each corpuscle possesses an oval nucleus (Hewson)[66], which projects into either concave surface of the whole corpuscle. These corpuscles do not possess the power of spontaneous movement; and have no cell-wall. The corpuscles are of a reddish-yellow colour, and give the blood its characteristic hue. The colouring matter is haemoglobin, and when separated it crystallizes in prisms (Preyer). The corpuscles show a well-marked intracellular and intranuclear network.]

[Footnote 66: Gulliver, Proc. Zool. Soc. London, 1845, Vol. XIII, p. 93 seq.]

[Footnote 67: Hewson, Phil. Trans. 1773, Vol. LXIII, p. 310 seq.]

B. [The *Lymph* and *Chyle*.

The *lymph* is that portion of the blood which has filtered from the blood-vessels, through the tissues, into the lymphatics. It is a clear, transparent fluid, containing colourless corpuscles, which agree in all particulars with the colourless corpuscles of the blood. During digestion the lymph from the alimentary canal contains particles of fatty matter, and is then known as *chyle*.] The colourless corpuscles of the lymph frequently contain portions of red corpuscles or granules of pigment. Non-nucleated masses of protoplasm and decolourised red corpuscles (slightly diminished in size) have also been described as occurring frequently in the lymph (Fuchs[68]).]

[Footnote 68: Fuchs, Virchow’s Arch. 1877, Vol. LXXI, p. 78 seq.]

C. [Histological Remarks on the Vascular System.

*a.* The *heart* has already been described (pp. 216–222).

*b.* The *blood-vessels* present the same structure as the corresponding vessels in higher animals. The _arteries_ and _veins_ have each the three walls or layers usually described--_Tunica adventitia_, _Tunica media_, and _Tunica intima_. The only characteristic to be mentioned is that the _Tunica adventitia_ contains branched, pigmented corpuscles. The _Nervi vasorum_, especially of the smaller arteries, are arranged in two plexuses, one in the _Tunica adventitia_ (His)[69], the second in the muscular coat (J. Arnold)[70]. The fibres of both plexuses are non-medullated, and have the usual beaded appearance; they communicate freely with each other. The *capillaries* present, as a rule, the usual structure: such special arrangements of the capillaries or peculiarities in structure as occur will be described with the organs in which they are found.

[Footnote 69: His, Virchow’s Arch. 1863, Vol. XXVIII, p. 427.]

[Footnote 70: Arnold, in Stricker’s Handbuch d. Gewebelehre, p. 137.]

*c.* The *subcutaneous lymph-sacs* are lined with a layer of endothelium resembling the endocardium shown in Fig. 140; the endothelial layer possesses stomata (see peritoneum), through which the lymph-sacs communicate with the underlying lymphatics. The endothelium is continued on to the vessels, nerves, etc., which course through the sacs, and excludes these from the cavities. As a rule an artery, vein, and nerve are enclosed in a common sheath.

*d.* The *lymph-hearts* are small saccular bodies with thin transparent walls, which contain obscurely striated muscle-fibres. The vessels communicating with the hearts appear to possess valves (Müller). The walls of the hearts are formed of three layers; an external, compared by Waldeyer to an _adventitia_, a muscular layer, and an endothelial lining. The muscular fibres form a close interlacing mass, the fibres being small, branched (Leydig), and possessed of many nuclei. Among the muscular fibres are pigmented corpuscles, together with medullated and non-medullated nerve-fibres, but no ganglion-cells (Volkmann, Waldeyer, Priestley). The _adventitia_ is a connective-tissue layer with many pigment cells (Leydig, Hyrtl, Waldeyer).]

SECTION V.

THE ALIMENTARY TRACT WITH ITS APPENDAGES, THE SPLEEN, AND THE PERITONEUM.

THE ALIMENTARY TRACT, ETC.

LITERATURE.

THE MOUTH.

(Except the mucous membrane of the tongue, for which see organ of taste.)

*Ducrotay de Blainville, H. M.*, Ostéographie ou description iconographique comparée du squelette et du système dentaire des cinq classes d’animaux vertébrés. Paris, 1841.

*Erdl*, Ueber den Bau der Zähne bei den Wirbelthieren, etc. München, 1841.

*Fixen, C.*, De linguae raninae structura. Dorpat, 1857.

*Heincke, F.*, Untersuchungen über die Zähne niederer Wirbelthiere. Zeitsch. f. wiss. Zool. 1873. Vol. XXIII, p. 495.

*Hertwig, O.*, Ueber das Zahnsystem der Amphibien, etc. Suppl. to Vol. XI, Arch. f. mik. Anat. 1874.

*Hoffmann, C. K.*, Bronn’s Thierbuch. Leipzig and Heidelberg, 1873–1878. Vol. VI, p. 379.

*Holl, M.*, Zur Anatomie der Mundhöhle von Rana temporaria. Wiener Acad. Sitzungsb. 1887. Vol. XCV, Pt. III, p. 47.

*Hoyer*, Ueber die Epithelzellen der Froschzunge, sowie über den Bau der Cylinder- und Flimmerepithelien und ihr Verhältniss zum Bindegewebe. Arch. f. Anat. u. Physiol. 1858, p. 163; also Deutsche Klinik, 1857.

*Langer, C.*, Ueber das Lymphgefässsystem des Frosches. Wiener Acad. Sitzungsb. 1867. Vol. LV, Pt. I, pp. 614–621.

*Leydig*, Die Anuren Batrachier der deutschen Fauna. Bonn, 1877.

*Owen, R.*, Odontography. London, 1840–1845, p. 187.

*Reichel, P.*, Beiträge zur Morphologie der Mundhöhlendrüsen der Wirbelthiere. Leipzig, 1882; also in Morph. Jahrb. 1882, Vol. VIII, pp. 1–72.

*Santi Sirena*, Untersuchungen über den Bau und die Entwicklung der Zähne bei den Amphibien und Reptilien. Verhandl. d. phys.-med. Gesellsch. in Würzburg, 1872. Vol. II, new series, p. 125.

*Schöbl, J.*, Ueber divertikelbildende Capillaren in der Rachenschleimhaut nackter Amphibien. Sitzungsb. d. k. b. Gesellsch. d. Wiss. in Prag. 1878, p. 25; also in Arch. f. mik. Anat. 1885, Vol. XXV, p. 89.

*Schultze, F. E.*, Das Drüsenepithel der schlauchförmigen Drüsen des Dünn- und Dickdarms und die Becherzellen (of the pharyngo-oral cavity). Centralbl. f. d. med. Wiss. 1866, p. 61.

*Schultze, F. E.*, Epithel- und Drüsen-Zellen. Arch. f. mik. Anat. 1867. Vol. III, p. 137.

*Smith, W. J.*, Beitrag zur differentiellen Diagnose der Rana fusca s. platyrrhinus und Rana arvalis s. oxyrrhinus auf Grund der an den Gaumenzähnen nachweisbaren Unterschiede. Pflüger’s Arch. f. d. ges. Physiol. 1883. Vol. XXXII, pp. 581–588.

*Tomes, C. S.*, On the development of the teeth of the newt, frog, slowworm, and green lizard. Phil. Trans. 1874, p. 285.

*Török*, Untersuchungen über die Entwickelung der Mundhöhle, etc. Wiener Sitzungsb. 1866. Vol. LIV, Pt. I, p. 75.

*Waller, A.*, Microscopic examination of the principal tissues of the tongue, etc. Phil. Mag. 1846, pp. 273–290.

*Waller, A.*, On the development of the mouth and tongue of the frog. Phil. Mag. 1850. Vol. I, pp. 38–43.

*Zeller, A.*, Die Abscheidung des indig.-schwefelsauren Natrons in den Drüsen (Intermaxillary gland). Virchow’s Arch. 1878. Vol. LXXIII, p. 257.

THE OESOPHAGUS AND STOMACH.

*Biedermann*, Untersuchungen über Magenepithel. Wiener Acad. Sitzungsb. 1875. Vol. LXXI, Pt. III, p. 377.

*Bischoff*, Ueber den Bau der Magenschleimhaut. Arch. f. Anat. u. Physiol. 1838, p. 503.

*Bleyer, E.*, Magenepithel und Magendrüsen der Batrachier. Dissert. Königsberg, 1874.

*Braun*, Zum Vorkommen von Flimmerepithel im Magen. Zool. Anzeiger. 1880. No. 69, p. 568.

*Brinton*, in Cyclopaedia of Anat. and Physiol., edited by R. B. Todd. 1859. Vol. I, p. 320.

*Cobelli*, Le gliandole acinose del cardia. Wiener Acad. Sitzungsb. 1866. Vol. LIII, Pt. I, p. 251.

*Ebstein, W.*, Beiträge zur Lehre vom Bau und den physiologischen Funktionen der sogenannten Magenschleimdrüsen. Arch. f. mik. Anat. 1870. Vol. VI, p. 515.

*Ecker, A.*, Ueber die Drüsen der Magenschleimhaut. Zeitsch. f. rat. Med. 1852, p. 243.

*Foster, M.*, On some points in the epithelium of the frog’s throat. Journ. of Anat. and Physiol. 1869. Vol. IV, p. 394.

*Frerichs*, On the Stomach, in Wagner’s Handwörterbuch d. Physiol. 1848. Vol. II, p. 748.

*Glinsky, A.*, Zur Kenntniss des Baues der Magenschleimhaut der Wirbelthiere. Centralbl. f. d. med. Wiss. 1883, p. 225.

*Gonjaew, K.*, Die Nerven des Nahrungsschlauches. Arch. f. mik. Anat. 1875. Vol. XI, pp. 479–496.

*Hebold, O.*, Ein Beitrag zur Lehre von der Sekretion und Regeneration der Schleimzellen. Dissert. Bonn, 1879, pp. 21–27.

*Heidenhain, R.*, Untersuchungen über den Bau der Labdrüsen. Arch. f. mik. Anat. 1870. Vol. VI, p. 368.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig und Heidelberg. 1873–1878. Vol. VI, pp. 408–412.

*Just, A.*, Zur Histologie und Physiologie des Flimmerepithels. Breslauer ärztliche Zeitsch. 1885. No. 18, pp. 205–206.

*Klein, E.*, Darmkanal, in Stricker’s Gewebelehre, p. 388, etc.

*v. Kölliker, A.*, Mikroskopische Anatomie, 1854. Vol. II, p. 147.

*Langley, J. N.*, and *Sewall, H.*, On the changes in pepsin-forming glands during secretion. Journ. of Physiol. 1880. Vol. II, pp. 261, 281.

*Langley, J. N.*, On the histology and physiology of pepsin-forming glands. Phil. Trans. 1881. Vol. CLXXII, Pt. III, pp. 663–712.

*Langley, J. N.*, On the structure of secretory cells and on changes which take place in them during secretion. Internat. Monatschr. f. Anat. u. Histol. Vol. I, pp. 69–76.

*Leydig*, Lehrbuch der Histologie. 1857.

*Nussbaum, M.*, Ueber den Bau und die Thätigkeit der Drüsen. Arch. f. mik. Anat. 1882, Vol. XXI, p. 296; 1882, Vol. XXVIII, p. 296; 1877, Vol. XIII, p. 721.

*Partsch, C.*, Beiträge zur Kenntniss des Vorderdarmes einiger Amphibien und Reptilien. Arch. f. mik. Anat. 1877. Vol. XIV, p. 179.

*Regéczy, E. N.*, Ueber die Epithelzellen des Magens. Arch. f. mik. Anat. 1880. Vol. XVIII, pp. 408–411.

*Robinson, C.*, Ueber die Lymphgefässe der Abdominaleingeweide des Frosches, etc. Froriep’s Notizen, 1846. No. 807, col. 225.

*Rollett*, Bemerkungen zur Kenntniss der Labdrüsen und der Magenschleimhaut. Untersuch. in d. Institut f. Physiol. u. Histol. zu Graz. 1871.

*Schultze, F. E.*, Epithel- und Drüsenzellen. Arch. f. mik. Anat. 1867. Vol. III, p. 174; abstract in Centralbl. f. med. Wiss. 1866, No. 4.

*Schmidt, C.*, Ueber eingenthümliche aus dem Flimmerepithel hervorgehende Gebilde. Arch. mik. Anat. 1881. Vol. XX, p. 123.

*Sewall, H.*, A note on the processes concerned in the secretion of the pepsin-forming glands of the frog. Studies in the Biol. Laborat., Johns Hopkins Univers. Vol. II, pp. 131–134.

*v. Swiecicki, H.*, Untersuchungen über die Bildung und Ausscheidung des Pepsins bei den Batrachiern. Pflüger’s Arch. f. d. ges. Physiol. 1876. Vol. XIII, p. 444.

*Trinkler, N.*, Zur Kenntniss des feineren Baues der Magenschleimhaut, insbesondere der Magendrüsen. Centralbl. f. med. Wiss. 1883, pp. 161–163.

*Trinkler, N.*, Ueber den Bau der Magenschleimhaut. Arch. f. mik. Anat. 1885. Vol. XXIV, p. 74.

*Trütschel*, Ueber die Endigung der Nerven in der Schleimhaut des Magens. Centralbl. f. d. med. Wiss. 1870, p. 115.

*Valatour*, Recherches sur les glandes gastriques et sur les tuniques musculaires du tube digestif dans les poissons ossieux et les Batraciens. Annales de Sc. nat. 1861. Series IV. Vol. XVI, p. 219.

THE INTESTINE.

*Arnstein, C.*, Ueber Becherzellen, etc. Virchow’s Arch. 1867. Vol. XXXIX, p. 527.

*Arnstein, C.*, and *Gonjaew, K.*, Ueber die Nerven des Verdauungskanals. Pflüger’s Arch. f. d. ges. Physiol. 1874. Vol. VIII, pp. 614–615.

*Auerbach, L.*, Fernere vorläufige Mittheilung über den Nervenapparat des Darmes. Virchow’s Arch. 1864. Vol. XXX, p. 457.

*Auerbach, L.*, Untersuchungen über Lymph- und Blutgefässe. Virchow’s Arch. 1865. Vol. XXXIII, p. 340.

*Auerbach, L.*, Organologische Studien.

*Billroth, T.*, Ueber die Epithelzellen der Froschzunge; der Bau, Cylinder- und Flimmerepithel und ihr Verhältniss zum Bindegewebe. Arch. f. Anat. u. Physiol. 1858, p. 159.

*Billroth, T.*, Einige Beobachtungen über das ausgedehnte Vorkommen von Nervenanastomosen im Tractus intestinalis. Arch. f. Anat. u. Physiol. 1858, p. 148.

*Brettauer* und *Steinach*, Untersuchungen über das Cylinderepithelium. Wiener Akad. Sitzungsb. 1857. Vol. XXIII, p. 303. Moleschott’s Zeitsch. 1857. Vol. III, p. 157.

*Darsch, O.*, Beiträge zur Kenntniss des feineren Baues des Dünndarms. Wiener Sitzungsb. 1880. Vol. LXXXII, Pt. III, p. 168.

*Dönitz*, Ueber die Schleimhaut des Darmcanals. Arch. f. Anat. u. Physiol. 1864, p. 367.

*Dönitz*, Ueber Darmzotten. Arch. f. Anat. u. Physiol. 1866, p. 757.

*Eberth, C. J.*, Ueber den feineren Bau der Darmschleimhaut. Würzb. naturw. Zeitschr. 1864. Vol. V, p. 23.

*Eimer, T.*, Zur Fettresorption, etc. Virchow’s Arch. 1867. Vol. XXXVIII, p. 428.

*Eimer, T.*, Ueber Becherzellen. Virchow’s Arch. 1868. Vol. XLII, p. 490.

*Eimer, T.*, Zur Geschichte der Becherzellen. Dissert. 1867.

*Eimer, T.*, Die Wege des Fettes in der Darmschleimhaut bei seiner Resorption. Virchow’s Arch. 1869. Vol. XLVIII, p. 119.

*Eimer, T.*, Zur Becherfrage. Virchow’s Arch. 1867. Vol. XL, p. 282.

*Erdmann*, Die Resorptionswege in der Schleimhaut des Dünndarms. Dissert. Dorpat, 1867.

*Fries, E.*, Ueber die Fettresorption und die Entstehung der Becherzellen. Virchow’s Arch. 1867. Vol. XL, p. 519.

*Gerlach, L.*, Ueber den Auerbachschen Plexus mysentericus. Arbeiten aus d. physiol. Anstalt. Leipzig. 1872, pp. 102–112.

*Gonjaew, K.*, Die Nerven des Nahrungsschlauches. Arch. f. mik. Anat. 1875. Vol. XI, pp. 479–496.

*Gruby* and *Delafond*, Résultats des recherches faites sur l’anatomie et les fonctions des villosités intestinales, etc. Compt. rend. 1843. Vol. XVI, p. 1194.

*Grugenhagen, A.*, Ueber Fettresorption und Darmepithel. Arch. f. mik. Anat. 1887. Vol. XXIX, p. 139.

*Heidenhain, R.*, Die Absorptionswege des Fettes. Moleschott’s Untersuchungen. 1858. Vol. IV, p. 251.

*Henle, J.*, Symbolae ad anatomiam villorum intestinalium impr. eorum epithelii et vasorum lacteorum. Berolini, 1837.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig und Heidelberg, 1873–1878. Vol. VI, pp. 412–424.

*Klein, E.*, Der Darmkanal in Stricker’s Gewebelehre, Article XVI.

*Klein, E.*, Contributions to the anatomy of Auerbach’s Plexus in the intestine of the frog and toad. Quart. Journ. Micros. Sci. 1873. Vol. XIII, p. 377.

*Klein, E.*, and *Verson, E.*, Der Darmcanal, in Stricker’s Gewebelehre, 1871, p. 355.

*Klein, E.*, Der neue Nervenapparat v. Thanhoffer’s. Centralbl. f. d. med. Wiss. 1883, p. 82.

*v. Kölliker, A.*, Nachweis eines besonderen Baues der Cylinderzellen des Dünndarms. Verhandl. d. phys.-med. Gesells. Würzburg, 1856. Vol. VI, p. 153.

*v. Kölliker, A.*, Handbuch der Gewebelehre.

*Lambl*, Ueber die Epithelialzellen der Dünndarmschleimhaut. Wiener med. Wochenschr. 1859. Nos. 24 and 25.

*Langer, C.*, Ueber das Lymphgefässsystem des Frosches. Wiener Acad. Sitzungsb. 1866. Vol. LIII, Pt. I, p. 395.

*Letzerich, L.*, Ueber die Resorption der verdauten Nährstoffe im Dünndarm. Virchow’s Archiv. 1866, Vol. XXXVII, p. 232; 1867, Vol. XXXIX, p. 435.

*Lipsky, A.*, Beitrag zur Kenntniss des feineren Baues des Darmcanals. Wiener Akad. Sitzungsb. 1865. Vol. LV, Pt. I, p. 183.

*Oeffinger*, Einige Bemerkungen über die sogenannten Becherzellen. Arch. f. Anat. u. Physiol. 1867, p. 337.

*Partsch, C.*, Beiträge zur Kenntniss des Vorderdarmes einiger Amphibien und Reptilien. Arch. f. mik. Anat. 1877. Vol. XIV, p. 179.

*Remak, R.*, Ueber peripherische Ganglien an den Nerven des Nahrungsrohrs. Arch. f. Anat. u. Physiol. 1858, p. 189; also in Zeit. d. Vereins f. Heilkunde in Preussen. 1840.

*Renzoni*, Osservazioni e ricerche sul epitelio intestinale. Rendiconti dell Acad. di Napoli. 1868.

*Rusconi*, Riflessioni sopra il sistema linfatico dei rettili. Pavia, 1845.

*Sachs, J.*, Zur Kenntniss der sogenannten Vacuolen oder Becherzellen im Dünndarm. Virchow’s Arch. 1867. Vol. XXXIX, p. 493.

*Schultze, F. E.*, Das Drüsenepithel der schlauchförmigen Drüsen des Dünn- und Dickdarms und die Becherzellen. Centralbl. f. d. med. Wiss. 1866, p. 160.

*Schultze, F. E.*, Epithel- und Drüsen-Zellen. Arch. f. mik. Anat. 1867. Vol. III, p. 145.

*Thanhoffer, L.*, Beiträge zur Fettresorption und histologischen Structur der Dünndarmzotten. Pflüger’s Arch. f. d. ges. Physiol. 1874. Vol. VIII, pp. 391–443.

*v. Thanhoffer, L.*, Ein neuer Nervenapparat im Dünndarm. Centralbl. f. d. med. Wiss. 1883, p. 33.

*v. Thanhoffer, L.*, Antwort auf Herrn Prof. Klein’s ‘Der neue Nervenapparat etc.,’ betitelte Bemerkungen. Centralbl. f. d. med. Wiss. 1883, p. 176.

*Valatour, M. M.*, Recherches sur les glandes gastriques et sur les tuniques musculaires du tube digestif dans les poissons et les Batraciens. Annales des Sci. nat. 4th Series, Vol. XVI. Zool. 1861, pp. 219–285.

*Watney, H.*, The minute anatomy of the alimentary canal. Phil. Trans. 1877. Vol. CLXVI, Pt. II, p. 451.

*Wiegandt*, Untersuchungen über das Dünndarmepithel. Dissert. Dorpat, 1860.

*v. Wittich*, Beiträge zur Frage über Fettresorption. Virchow’s Arch. 1857. Vol. XI, p. 37.

THE LIVER, GALL-BLADDER, AND PANCREAS.

*Barfurth, D.*, Vergleichend-histochemische Untersuchungen über das Glycogen. Arch. f. mik. Anat. 1885. Vol. XXV, p. 369.

*Brotz, J.*, and *Wagenmann, C. A.*, De amphibiorum hepate et glandularum ductu excretio carentium structura deque earundem functionibus experimenta. Berolini, 1841.

*v. Brunn, A.*, Flimmerepithel in den Gallengängen des Frosches. Zool. Anzeiger. 1883. No. 148, p. 483.

*Eberth, C. J.*, Die Pigmentleber der Frösche und die Melanämie. Virchow’s Arch. 1867. Vol. XL, p. 305.

*Eberth, C. J.*, Zur Kenntniss der Verbreitung glatter Muskeln. Zeitschr. f. wiss. Zool. 1863. Vol. XII, p. 360.

*Eberth, C. J.*, Ueber den feineren Bau der Leber. Centralbl. f. d. med. Wiss. 1866, p. 897.

*Eberth, C. J.*, Untersuchungen über die Leber der Wirbelthiere. Arch. f. mik. Anat. 1867. Vol. III, p. 423.

*Eberth, C. J.*, Untersuchungen über die normale und pathologische Leber. Virchow’s Arch. 1867. Vol. XXXIX, p. 70.

*Eberth, C. J.*, Ueber die Pigmentleber der Frösche. Virchow’s Arch. 1862. Vol. XXIX, p. 70.

*Gerlach, L.*, Ueber die Nerven der Gallenblase. Centralbl. f. d. med. Wiss. 1873, p. 562.

*Hering, E.*, Ueber den Bau der Wirbelthierleber. Wiener Acad. Sitzungsb. 1886. Vol. LIV, Pt. I, p. 335.

*Hering, E.*, Ueber den Bau der Wirbelthierleber. Arch. f. mik. Anat. 1867. Vol. III, p. 88.

*Hering, E.*, On the liver. Stricker’s Gewebelehre. 1872, p. 429.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig und Heidelberg, 1873–1878. Vol. VI, p. 424.

*Jones, C. H.*, On the structure and development of the liver. Phil. Trans. 1849. Pt. I, p. 122.

*Langley, J. N.*, On variations in the amount and distribution of fat in the liver-cells of the frog. Proc. Roy. Soc. 1886. Vol. XXXIX, p. 234.

*Leydig, F.*, Lehrbuch der Histologie. 1857.

*Leydig, F.*, Die Leber der Fische und Batrachier.

*Nussbaum, M.*, Ueber den Bau und die Thätigkeit der Drüsen (Pancreas). Arch. f. mik. Anat. 1877. Vol. XIII, p. 752.

*Popoff, M.*, The nerves of the gall-bladder (in Russian). Rudneff’s Journ. f. normal. u. pathol. Histol., etc. 1872.

*Remak, R.*, Ueber runde Blutgerinnsel und über pigmenthaltige Zellen. Arch. f. Anat. u. Physiol. 1852, p. 115.

*Weber, E. H.*, Ueber die periodische Farbenänderung welche die Leber der Hühner und Frösche erleidet. Bericht von Verhandl. K. Säch Gesell. Leipzig, 1850, p. 15.

*Zeller, A.*, Die Abscheidung des indig.-schwefelsauren Natrons in den Drüsen (Pancreas). Virchow’s Arch. 1878. Vol. LXXIII, p. 257.

THE SPLEEN.

*Billroth, T.*, Beiträge zur vergleichenden Anatomie der Milz. Arch. f. Anat. u. Physiol. 1857, p. 88.

*Billroth, T.*, Beiträge zur vergleichenden Anatomie der Milz. Virchow’s Arch. 1861, Vol. XX, p. 410, and 1862, Vol. XXIII, p. 457; also Zeitschr. f. wiss. Zool. 1862, Vol. XI, p. 325.

*Ecker*, Blutgefässdrüsen, in Wagner’s Handwörterbuch der Physiologie. 1849. Vol. IV.

*Gray, H.*, On the structure and use of the spleen. London, 1854.

*Hoffmann, C. K.*, Bronn’s Thierbuch. Leipzig und Heidelberg, 1873–1878. Vol. VI, p. 509.

*v. Kölliker, A.*, Ueber den Bau und die Verrichtungen der Milz. Mittheil. d. naturf. Gesell. in Zürich, 1847. Vol. I, p. 120.

*Kusnezoff, F.*, Ueber blutkörperchenhaltige Zellen der Milz. Wiener Sitzungsber. 1873. Vol. LXVII, Pt. III, pp. 58–67.

*Müller, W.*, Ueber den feineren Bau der Milz. Leipzig und Heidelberg, 1865.

*Remak, R.*, Ueber runde Blutgerinnsel und über pigmenthaltige Zellen. Arch. f. Anat. u. Physiol. 1852, p. 115.

*Schweigger-Seidel, F.*, Untersuchungen über die Milz. Virchow’s Arch. 1862. Vol. XXIII, p. 526.

*Stieda, L.*, Zur Histologie der Milz. Dorpat, 1862.

THE PERITONEUM.

*Alltmann, R.*, Ueber die Veränderungen des serösen Epithels am blosgelegten Froschmesenterium. Arch. f. mik. Anat. 1878. Vol. XVI, p. 111.

*Arnold, J.*, Ueber die Durchtrittsstellen der Wanderzellen durch entzündete seröse Häute. Virchow’s Arch. 1878. Vol. LXXIV, p. 245.

*Batelli, A.*, Dello addaltamento di alcune cellule endotiali nelle membrane serose. Lo Sperimentale. 1884, p. 132.

*Cyon*, Ueber die Nerven des Peritoneum. Bericht über d. Verhandl. d. Kön. Säch. Gesell. d. Wiss. z. Leipzig, 1868. Vol. XX, p. 119. Leipzig, 1869.

*Grunau, H.*, Ueber das Flimmerepithel auf dem Bauchfell des weiblichen Frosches und über den Eileiterbau desselben. Dissert. Königsberg, 1875.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig und Heidelberg, 1873–1878. Vol. VI.

*Hoffmann, T.*, Die Lungen-Lymphgefässe der Rana temporaria. Dissert. Dorpat, 1875.

*Kapff*, Untersuchungen über das Ovarium und dessen Beziehungen zum Peritoneum. Arch. f. Anat. u. Physiol. 1872, p. 553.

*Klein, E.*, On Remak’s ciliated vesicles and corneous filaments of the peritoneum of the frog. Quart. Journ. Mic. Sci. New Series, 1872. Vol. XII, p. 43.

*Klein, E.*, On the peripheral distribution of non-medullated nerve-fibres (nerves of the peritoneum). Quart. Journ. Micros. Sci. 1872. Vol. XII, p. 32.

*Leydig*, Lehrbuch der Histologie. 1857, p. 325.

*Mayer*, Ueber die Flimmerbewegung. Froriep’s Notizen, 1836. Vol. XLVII, p. 179.

*Neumann, E.*, Die Beziehungen des Flimmerepithels der Bauchhöhle zum Eileiterepithel beim Frosch. Arch. f. mik. Anat. 1875. Vol. XI, pp. 354–377.

*Nicolsky, P.*, Ueber das Flimmerepithel beim Frosche. Centralbl. f. d. med. Wiss. 1880, p. 641.

*Paladino, G.*, Dell’ endotelio vibratile nei Mammiferi ed in generale di alcuni dati sulla fisiologia delle formazioni endoteliche. Estr. dal Giornale intern. delle Scienze Mediche. 1882. Vol. IV.

*Schweigger-Seidel* and *Dogiel*, Ueber die Peritonealhöhle der Frösche. Arbeiten aus d. physiol. Anstalt zu Leipzig. 1866, p. 68.

*Solger, B.*, Ueber einige Entwicklungsstadien des Peritonealepithels der Amphibien-larven. Manusc. d. Naturf. Versamml. zu Freiburg. 1884.

*Thiry*, Ueber das Vorkommen eines Flimmerepitheliums auf dem Bauchfell des weiblichen Frosches. Göttinger Nachrichten. 1862, pp. 171–174.

*Tourneux*, Recherches sur l’épithelium des sereuses. Journ. de l’anat. et de la physiol. 1874.

*Waldeyer*, Eierstock und Ei. Leipzig, 1870, pp. 72 and 122.

*Wolff, W.*, Ueber freie sensible Nervenendigungen. Arch. f. mik. Anat. 1882. Vol. XX, pp. 377–381.

THE ALIMENTARY TRACT, ETC.

I. THE ALIMENTARY TRACT.

The alimentary tract consists of the mouth or pharyngo-oral cavity, the oesophagus, the stomach, the small intestine and the large intestine; these together forming a tube extending from the mouth to the cloaca. From the commencement of the oesophagus, at the entrance to the larynx, to the end of the cloaca, the length of the tube is about 31.5 cm., that of the various parts being:

From glottis to pylorus 5.5 cm. From pylorus to large intestine 22.0 cm. Large intestine to end of cloaca 4.0 cm. -------- Total length 31.5 cm. ========

A. The *Mouth*.

The mucous membrane covering the tongue will be described with the sense-organs (see organ of taste).

*a.* *General description.* The mouth of _R. esculenta_, as in all other amphibia, with the exception of the lowest (_Siren_, _Proteus_, etc.), is of considerable width, and extends backwards as far as the middle of the tympanic membrane. The upper margin of the mouth possesses a lip or fold of the skin (_SS^{1}_), which projects sufficiently to prevent the teeth being seen from the front or from the sides. This lip-like rim is most prominent in the premaxillary and superior maxillary regions, but can be traced along the whole length of the upper jaw, and on to the lower jaw, by means of a well-marked fold at the angle of the mouth. Beyond this point the lip is absent, as the skin is closely attached to the bony mandible.

On the *roof* of the *mouth* the following structures can be made out: immediately within the lip is a deep, well-marked groove, the outer boundary formed by the lip, the inner by a fold of the mucous membrane (Fig. 178 _F_); this fold increases from behind forwards as far as the premaxillary bones, where it forms two prominences (_F^1_, _F^1_) with an interval between. These correspond to the palatine processes of the premaxillary bones: immediately behind them are openings of the ducts of the intermaxillary glands. In the groove so formed are placed a single row of simple teeth, which, though subject to many variations, are usually about fifty in number.

[Illustration: Fig. 178.

The roof of the mouth.

_Cho_ Posterior naris. _ID_ Opening of intermaxillary glands. _F_ Fold of mucous membrane. _F^1_, _F^1_ Prominences of mucous membrane. _K_ Muscles. _O_ Floor of the orbit. _S_ Lip. _S^1_ Lip. _T_ Eustachian tubes. _Vo_ Vomer. ]

A little further back and to either side of the median line is a small group of vomerine teeth (_Vo_); each group has from five to ten teeth; external to these is on each side a transversely-placed oval opening, the posterior nares (_Cho_). These apertures are directed outwards and backwards into a shallow groove, bounded anteriorly by a fold of mucous membrane.

According to Wiedersheim the mucous membrane immediately around the vomerine teeth is supplied with taste-bulbs; the epithelium surrounding these being non-ciliated.

The roof of the mouth underneath the parasphenoid is somewhat vaulted and on either side depressed by the eyeballs, which project downwards more or less prominently (_O_, _O_). Still further back are the openings of the Eustachian tubes (Fig. 178 _T_), one on each side, and almost surrounded by the limbs of the pterygoid bones.

On the *floor* of the *mouth* (Fig. 179) the tongue (_Z_, _Z^1_) forms the most prominent object; its shape varying according to the state of contraction of its muscles. Behind it, in the middle line, is a transverse groove (†), corresponding to the posterior border of the hyoid bone, and still further back is the opening to the larynx (_L_), a longitudinal slit about 3 mm. in length. The mucous membrane to either side of the tongue is only slightly folded, and a little in front of the angle of the mouth is depressed into an aperture (_S_), opening into the vocal sac. This opening is surrounded by small radiating folds of mucous membrane, and is oval in shape.

[Illustration: Fig. 179.

The floor of the mouth.

_K_ Muscles. _L_ Opening to larynx. _M_ Mandible. _S_ Opening to voice-sac (in males only) _Sm_ Chin. _Z_ Tongue. _Z^1_ Left cornu of bifid tongue. † Folds opposite hinder border of the hyoid. ]

Towards the oesophagus the mucous membrane of both the roof and the floor of the mouth is thrown into numerous longitudinal folds.

*b.* The *minute structure* of the several parts.

(1) The *mucous membrane* of the mouth. At the junction of the skin and the mucous membrane there is a gradual transition from the stratified epithelium of the skin to a single layer of *columnar epithelium*. On the floor of the mouth this condition is reached at the tongue; on the roof the transition takes place more quickly. The columnar epithelium of the mouth (that of the tongue is excluded from this description) is ciliated; scattered cells, which are not ciliated, are found here and there irregularly, but are not numerous. The cylindrical cells are very finely granular in their upper parts, clearer in the middle portion, more coarsely and darkly granular in their deeper portions; each cell is possessed of a large, well-defined, oval nucleus, which contains one or sometimes two nucleoli. The non-ciliated cells usually present a sharply differentiated, structureless, hyaline, free border (Schultze). The epithelium towards the margin of the mouth, where it is stratified, is also ciliated.

Goblet-cells occur in every part of the epithelium, whether ciliated or non-ciliated, and their forms vary very greatly.

[The *submucous layer* is a fibrous connective-tissue matrix, very rich in nerves and blood-vessels. The capillaries are arranged in small, somewhat polygonal meshes (Fig. 180), and are peculiar, with those of the anterior part of the oesophagus, in having small dilatations. This arrangement was first[71] described by Langer, and later by Schöbl. The dilatations are placed quite irregularly on the capillaries, sometimes only on one side, sometimes on both sides of the vessel; a slight constriction occurs at the neck of each dilatation, where it opens into the capillary[72]. The nerves of the mucous membrane underneath the orbits have nerve-cells attached to them (Stirling and Macdonald, page 170). The lymphatics are very numerous, and for the most part follow the course of the blood-vessels to their finest twigs, beyond which they follow an independent course (Langer).]

[Footnote 71: Beale, Phil. Trans., 1863, p. 153, shows dilatations in his drawing, but makes no reference to them in the text.]

[Footnote 72: The vascular supply of the mucous membrane of the dorsal surface of the mouth and oesophagus is shown (after Schöbl) in Plate II, Fig. 180, I. Arteries red, veins blue. II. in the same figure represents the dilatations on the capillaries; after Schöbl.]

(2) The *teeth* are wanting in the lower jaw; on the roof of the mouth they are found in two situations: as a single row in the groove within the lip, and a group on each vomer. Each tooth has the form of an elongated cone, which in the case of the jaw-teeth is curved, in that of the vomerine teeth straight. The teeth are fixed to the jaw so as to project upwards and slightly inwards, those at the front of the mouth projecting backwards, and those on the vomers project backwards. Each tooth has a small, sharp projection, or secondary crown on its outer surface (Fig. 181), placed near the mucous membrane. The teeth are fixed to the bones by means of _Crusta petrosa_, which is again united to the bones of the mandible by a matrix of spongy bone, continuous for the several teeth. Between the tooth and the mucous membrane is a layer of flattened epithelium (_II_), which extends more deeply on the inner side of the tooth than on the outer; the layer is continuous with the epithelium of the mouth, and is two to three cells in thickness. Each tooth has fine longitudinal grooves on the basal part of its outer surface, and consists of two parts, a crown and a root. The teeth possess large cavities, the wall being thin and almost of even thickness, except on the inner surface of the basal portion of the root, where the wall is wanting, and so forms a large aperture to the root.

The general skeleton of the tooth is formed of dentine, this is covered on the crown by a layer of enamel, and the _Cuticula dentis_ on the socket by a layer of _Crusta petrosa_.

α. The *dentine* is a homogeneous substance pierced by numerous tubules (_D_), which arise at the pulp-cavity and course in a parallel direction to the surface of the dentine, where they form a rich network with irregular, interglomerular spaces. The inner surface of the dentine is rough, through the presence of numerous small, dark tubercles.

β. The *enamel* covers the dentine on the apical portion of the tooth. It has tubes coursing through it, which are continuous with those of the dentine, and presents also circumferential striations (Fig. 181 III).

[Illustration: Fig. 181.

I. Transverse section of the premaxillary bone to show attachment of the teeth; after Hertwig. Magnified 22 times.

II. Dentine and enamel; after Hertwig. Magnified 500 times.

III. Enamel: after Hertwig. Magnified 500 times.

_A_ Blood-vessel of the pulp-cavity. _C_ Crusta petrosa. _D_ Dentine. _F_ Processus dentalis. _H_ Layer of epithelium. _O_ Tooth cuticle. _R_ Reserve. _S_ Enamel. _X_ Cutaneous glands. ]

γ. The *tooth cuticle* (_Cuticula dentis_) is colourless and covers the enamel. It is highly refractive, very transparent, and very resistant to chemical reagents. From the apex, towards the _Crusta petrosa_, it thins very rapidly, but is continued sufficiently far to cover a portion of the _Crusta petrosa_.

δ. The _Crusta petrosa_ resembles bone, except that it contains no Haversian canals; it possesses cells which resemble bone corpuscles, and are usually somewhat rounded or oval and communicate with each other by their processes; for the most part it is homogeneous and free from cells (Hertwig).

ε. The *pulp-cavity* contains a connective-tissue very rich in cellular elements; those cells adjacent to the dentine are arranged in a layer (_Membrana eboris_) which has somewhat the appearance of a layer of epithelium. The cells (odontoblasts) of this layer are spindle-shaped, and send processes (dentinal fibres) into the dentinal tubules. A small blood-vessel can be traced into each cavity, but as yet no nerve has been found in the pulp-cavities.

[Smith (_l. c._) has, after careful investigation, come to the conclusion that the teeth of _R. esculenta_ and _R. temporaria_ are practically alike, therefore the methods of differentiating the two species by means of the teeth, as given by Leydig, are not to be relied on.]

(3) The *intermaxillary glands* (_Glandula intermaxillaris_) consist of a mass of convoluted tubes, lying chiefly between the premaxillary bones and the capsule of the nose, and opening by about twenty to twenty-five ducts at the fore-part of the mouth (Fig. 178 _ID_). A portion of the glands extends high into the nasal cavity (Born), while dorsally another portion lies under the skin and the _M. dilatator_ and _M. lateralis narium_, which together act as compressors to the subjacent glands: a small, elastic, cartilaginous rod, placed between the anterior margin of the nasal capsule and the under surface of the ascending limb of the premaxilla, opposes these muscles on either side by its spring-like action (Wiedersheim).

In a fresh skull the openings of the ducts can easily be seen after washing away the mucous secretion; they are, however, seen to better advantage by treatment with Müller’s fluid and subsequent staining with carmine. With sufficient magnifying power, they are then seen as a row of bright dots. The tubules are of uniform thickness, placed closely side by side, and surrounded by a nervous plexus, which contains numerous branching nerve-cells. The epithelium of the tubules is cylindrical, with a rounded, finely granular nucleus; processes from the peripheral ends of the cells are continued to a _Membrana propria_. The ducts are lined with columnar, ciliated epithelium.

The *secretion* of the glands is remarkably adhesive, and is wiped off by the tongue when it is projected; by this means the tongue becomes a particularly efficacious instrument for capturing prey. The glands are, both histologically and chemically, pure mucous glands. In urodeles the homologous glands are placed in the hollow septum of the nose, between the nasal cavities.

(4) The *tongue* (Figs. 179, 182, 183) is a broad, fleshy flap on the floor of the mouth, to which it is attached by the anterior half of its ventral surface as far forwards as the chin. Seen from above it has a wedge-like form, being narrow in front and wider behind, where it is prolonged at each angle to form two cornua.

By raising the tongue one obtains a view of a portion of the _M. hyoglossus_. The two _MM. hyoglossi_ arise (see page 66) some distance apart, and run forwards and towards each other to meet on the ventral surface of the hyoid bone; they now assume a longitudinal direction, and course forwards parallel to each other until they reach the _M. genio-glossus_ (Fig. 182 _G_). Each muscle now divides to form coarse bundles, which ascend on either side of the _M. genio-glossus_ towards the dorsum of the tongue. In this course they are encircled by a strong, elastic, connective-tissue sheath. The sheath is incomplete at the hinder end of the _M. genio-glossus_, where it possesses rounded apertures, through which the glossopharyngeal nerves (_N_, _N_) disappear, to be distributed, after a sharp curve backwards, in the substance of the organ.

The _M. genio-glossus_ arises, in two parts on either side, at the side of the chin. One part (Fig. 182 _G_) is dorsal and median, the other (Fig. 182 _G^1_) ventral and external.

[Illustration: Fig. 182.

Muscles of the tongue, seen from the ventral surface.

_G_ Median portion of M. genio-glossus. _G^1_ Lateral portion of M. genio-glossus. _H_ Hyoid. _Hy_ M. hyoglossus. _L_ Larynx. _M_ Mandible. _N_ Glossopharyngeal nerve. ]

The first part, with its fellow of the opposite side, forms an arched commissure in the form of muscular rings, which decrease in size from before backwards, and so form a pear-shaped mass: the second, external portion, extends backwards, with a slight obliquity, as a thin, fan-like expansion, to the mucous membrane, where it is inserted. This arrangement can easily be seen after dissecting away the sheath (Fig. 183 _Hy_); the hindermost fibres curve sharply into the tongue (_Hy^1_); the anterior fibres pass obliquely forwards and blend with the straight fibres of the dorsal portion of the _M. genio-glossus_ (Fig. 183 _Gg_). The arcuate fibres of the _M. genio-glossus_ pass, for the most part, upwards and outwards to the tips of the posterior bifid border of the tongue; in this course they lie as a rule above the _M. hyoglossus_, but here and there the two muscles intermix (Fig. 183 _Gg^1_), and it is by no means easy to separate them.

The _M. hyoglossus_ is the retractor of the tongue, the _M. genio-glossus_ the protractor.

(For mucous membrane of the tongue, see organ of taste. The vocal sacs are described with the organs of voice and respiration.)

B. The *Oesophagus* and *Stomach* (Figs. 184, 185, 189, 194, 195, 199).

*a.* *General description.* The oesophagus is not separated from the pharyngo-oral cavity by a sharp line of demarcation. It has a length of only a few mm. in medium-sized frogs (Fig. 184 _Oe_), and lies in the middle line of the body, supported on either side by the cornua of the hyoid bone. The oesophagus lies on the dorsal wall of the larynx, is smooth externally, and is thrown into well-marked longitudinal folds internally.

[Illustration: Fig. 183.

Muscles of the tongue, from the ventral surface.

_G_ M. genio-glossus. _Gg_ Straight fibres of the M. genio-glossus. _Gg^1_ Curved fibres of the M. genio-glossus. _Hy_ and _Hy^1_ M. hyoglossus. _Z_ Borders of the tongue. ]

The transition from oesophagus to stomach is somewhat indefinitely marked by a slight dilatation of the tube, often scarcely perceptible, still it can always be recognized by an abrupt curvature to the left (Fig. 184 _M_), which becomes more prominent when the stomach is distended. Externally the stomach is seen as an elongated, slightly curved cone, smooth externally and of equal diameter throughout.

The oesophagus and stomach are held in position by folds of peritoneum (mesentery), which attaches them to the dorsal wall of the abdominal cavity, to the lungs, pericardium, and liver; and by the blood-vessels.

*b.* *Minute structure.* The walls of these viscera are composed of four layers or coats.

(1) The *serous coat* (Fig. 186) is a layer of endothelium, lying on a very thin stratum of connective-tissue; the whole derived from the peritoneum, which encloses the organs.

(2) The *muscular coat* (Fig. 186 _LM_ and _TM_) is arranged in two layers, one (_LM_) longitudinal, the other (_TM_) transverse. The longitudinal layer is thicker in the oesophagus, and thins as it is continued to the pyloric end of the stomach. The circular layer, on the other hand, gains in thickness; both layers are of unstriated muscular fibre.

[Illustration: Fig. 184.

The alimentary canal.

_A_ Opening of large intestine into cloaca. _Cl_ Cloaca. _D_ Small intestine. _Du_ Duodenum. _HB_ Urinary bladder. _M_ Stomach. _Mz_ Spleen. _Oe_ Oesophagus. _Py_ Pylorus. _R_ Large intestine (rectum). † Junction of small and large intestine. ]

(3) The *submucous coat* (Fig. 186 _A_, _B_, and _SM_) is better developed in the stomach than in any other part of the alimentary canal. It is formed of a wide-meshed, loose connective-tissue, which supports numerous blood-vessels and lymphatics. Towards the mucous coat it possesses a well-differentiated _Muscularis mucosa_, which is arranged in two layers, a longitudinal (_B_) and a transverse (_A_).

(4) The *mucous coat* is possessed of numerous tubular glands, which vary in structure according to the part of the membrane examined. They have been the subject of much investigation (Heidenhain, Nussbaum, Partsch, Langley, and others), and are best described in three groups: those of the oesophagus, of the first part of the stomach, and of the pyloric end of the stomach respectively; between each pair of groups are transitional forms.

α. [The oesophageal glands are complete tubular glands lined by a single layer of epithelium, which very closely resemble the glandular cells of the fundus of the stomach (Plate II, Fig. 187). The cells are conical or cylindrical, the protoplasmic contents granular, the granules being larger than those of the corresponding cells in the stomach (Langley). Mucous cells are found among the true secretory cells. The cells of the ducts are sometimes, but rarely, ciliated (Langley).]

[Illustration: Fig. 185.

The abdominal viscera of _Rana esculenta_ (female).

_D_ Small intestine. _Du_ Duodenum. _EE_ Ovaries. _H_ Heart. _HB_ Urinary bladder. _L_ Left lobe of liver. _L^1_ Right lobe of liver. _L^2_ Middle lobe of liver. _Lg_ Left lung. _Lg^1_ Right lung. _M_ Stomach. ]

β. [The glands of the fundus of the stomach[73] are not so complex as the typical glands of the oesophagus. The cells at the mouth of the gland are continued into fine processes (Fig. 187), and their outer parts contain mucigen. The cells of the neck of the gland are more cubical, and towards the lower part of the neck are mucous cells. The cells of the body of the gland are of irregular shape, and so placed that the nucleus of one cell faces the junction of two cells on the opposite side (Langley). These cells are very finely granular.]

[Footnote 73: A transverse section through the mucous membrane of the fundus of the stomach of _Rana esculenta_ is shown in Plate II, Fig. 187. Alcohol preparation, doubly stained with carmine and anilin blue. After Biedermann. (Obj. II, Syst. 7, Hartnack.)]

[Illustration: Fig. 186.

Transverse section through one of the longitudinal folds of stomach of _Rana temporaria_. To show general arrangement of the walls.--G. H.

_A_ Transverse layer of muscularis mucosae. _B_ Longitudinal layer of muscularis mucosae. _LM_ Longitudinal muscular coat. _M_ Mucous membrane. _SM_ Submucous coat. _TM_ Transverse muscular coat. ]

γ. [The glands of the pyloric end of the stomach have been compared with the mouths and necks of the glands of the fundus (Partsch, Langley). The cells are of two kinds only (Fig. 188). The cylindrical cells of the surface of the stomach are continued into the gland, where they become shorter and sub-cubical; these form the greater part of the gland. The cells at the deepest portion of the gland are more rounded, and resemble the mucous cells in the neck of the glands of the fundus.]

δ. [Between these well-marked groups of glands are various transitional forms. The transition from oesophageal to gastric glands is not a continuous one, as glands resembling those of the stomach can be found nearer the oesophagus than other glands, which more nearly resemble oesophageal glands. At the same point the mucous membrane is thinner than either in front or behind. In the same way an intermediate zone exists between the typical glands of the fundus and pylorus of the stomach.]

In both oesophagus and stomach the mucous membrane is thrown into longitudinal folds when the organs are empty. The epithelium of the surface of the oesophagus is mostly ciliated, and possesses numerous goblet-cells; according to Klein the cells are not set vertically on the subjacent submucosa, but obliquely.

[The epithelium of the surface of the stomach is, at least in part, ciliated (Regéczy, Trinkler, and others), and has numerous goblet-cells (Schultze, Heidenhain, Bleyer, Eimer, Oedmonson, and others).]

[Illustration: Fig. 188.

Transverse section through the mucous membrane of the pyloric end of the stomach of _Rana esculenta_. After Partsch. (Obj. II, Syst. 7, Hartnack.) ]

(5) [The *nerves* of these organs, according to Gonjaew, contain both medullated and non-medullated fibres, which have nerve-cells attached to them. From these fine branches pass, either with the blood-vessels or alone, to the mucous coat, losing their medulla on the way. In this course they inosculate very freely, and are then distributed as very fine, beaded fibrils to the glands and epithelium, which are very richly supplied.]

(6) [The *blood-vessels* and *lymphatics* very closely resemble the corresponding structures in the small intestine (p. 290); the blood-vessels form a rich anastomosis in the submucous membrane; the lymphatics are arranged in two systems, one under the serous coat, and a larger system in the mucous and submucous coats. The oesophagus lies free in a peri-oesophageal lymph-sac (Robinson).]

C. The *Small Intestine*.

*a. General description.* The small intestine commences behind the middle of the abdomen at the pyloric end of the stomach, from which it is marked off by a slight constriction. The first portion of the small intestine is the duodenum (Figs. 184 and 194 _Du_); by means of an abrupt turn it winds directly forwards, parallel to the long axis of the stomach; the pancreas is placed in the loop so formed.

The whole of this portion of the intestine, together with the greater part of the stomach, is, in the normal condition, under cover of the liver (Figs. 185, 194): while under the liver the intestine is firmly attached to the deep surface of that organ by a short but strong _Ligamentum hepato-duodenale_; it then turns suddenly backwards, increases in size, and by means of numerous convolutions occupies a considerable portion of the right half of the abdomen (Fig. 184 _D_). It is held in position by a well-developed mesentery.

*b.* *Minute structure.* Like other portions of the alimentary canal, the small intestine is formed of four layers:--

(1) The *serous coat* presents no peculiarities; it consists simply of a layer of endothelial cells, with a small amount of sub-endothelial connective-tissue.

(2) The *muscular coat* is in two layers, the outer longitudinal layer being very thin, the inner circular layer thick.

(3) The *submucous layer* resembles that of the stomach, but is not so thick; the _muscularis mucosae_ is well developed and arranged, as in the stomach, in two layers.

(4) The *mucous coat* (Fig. 189) is thrown into folds, which differ in various parts of the tube.

The longitudinal folds of the stomach are compressed together towards the pyloric end of the stomach (_a_) and diminish in size; at the commencement of the duodenum they end abruptly (_a^1_), but without any indication of a valvular arrangement.

Immediately beyond the pylorus the mucous membrane is folded so as to form an irregular network of folds which inclose irregular alveoli; the folds are thicker on the concave surface of the duodenum, and form a longitudinal ridge (_b_); in this ridge the alveolar spaces are much smaller than those to either side. The irregular folding extends through two to three cm., when a more regular arrangement commences in the form of two adjacent series of transverse folds (_c, c^1_). Each fold is semi-lunar in shape, with the convexity attached to the wall of the tube and directed forwards, while the concave free border and pocket-like space enclosed are directed backwards.

The arrangement of these folds reminds one of the semi-lunar valves of the human heart, and probably one of their functions is to prevent the regurgitation of the chyme (Wiedersheim).

The corresponding valves of opposite sides meet at each end at an angle, the apex of which is directed away from the stomach. On these folds and between them are smaller, secondary folds, partly irregularly arranged, partly longitudinal (_d d_).

Towards the middle of the small intestine this valvular arrangement is lost, to be replaced by an irregular net-like folding; beyond this longitudinal folds arise, which proceed in a sinuous course towards the large intestine.

The whole mucous membrane, both on the folds and otherwise, is covered with a simple layer of columnar epithelium, which is continued into numerous simple follicles (glands of Lieberkühn) found throughout the mucous membrane of the small intestine. The cells are placed on a basement membrane, which rests on a thin layer of loose connective-tissue, intervening between the epithelial coat and the _muscularis mucosae_. The epithelial cells are intermixed with a large number of goblet-cells, and have between them fine processes from the connective-tissue corpuscles of the subjacent layer; many of these processes extend to or even beyond the free margin of the epithelial cells.

[Illustration: Fig. 189.

Mucous membrane of the pyloric end of the stomach and the duodenum.

_a_ Mucous membrane of the stomach. _a^1_ Commencement of duodenum. _b_ Duodenal mucous membrane arranged in irregular network. _c_ } Semi-lunar folds of _c^1_} the mucous membrane. _d_ Longitudinal folds of the mucous membrane. ]

The individual cells are columnar, possessed of a well-marked cell-wall, and have distinct, large, oval nuclei, containing one or more nucleoli. The protoplasmic contents are granular, and with proper treatment show a very distinct intracellular network. The free margins of the cells are sharply marked off from the cell-contents, and are more firmly attached to the corresponding portions of adjacent cells than the rest of the cell-wall. This margin has a longitudinal striation, which owing to the important function performed by this part of the intestine, namely, absorption of the fat, has been the subject of many important investigations.

[In the following brief summary of the earlier researches on the minute structure of the intestinal epithelium, in which the intestine of the frog was chiefly used, the memoirs in which these investigations are recorded are referred to in the order of time.

1837. Henle first described the border as a thickened, highly refractive portion of the cell-wall.

1855. Kölliker and Funke, after independent research, described the longitudinal striation: Funke offered no explanation of the fact, while Kölliker considered it due to the presence of fine tubules. Later Funke gave a modified support to Kölliker’s view by admitting the presence of tubules around the circumferential part of the border.

1856. Donders gave a description corresponding with that of Henle.

1857. Brettauer and Steinach gave it as the result of their investigations that the border was composed of closely-applied fine rods: v. Wittich first showed that the borders of adjacent cells were more firmly attached than the rest of the cell; he admitted the presence of apertures, but considered the whole appearance to be due to post-mortem changes.

Welcker and Friedreich agreed with the views of Brettauer and Steinach, but traced the striation throughout the length of the cells, in fact traced the tubules to the connective-tissue below.

1858. In this year Heidenhain published his results; he held the striation to be due to the presence of fine rods, and was the first to show that processes of the connective-tissue corpuscles passed up between the epithelial cells; he found fat globules in the epithelial cells, in the connective-tissue, and in the lacteals.

Friedreich described the striation as continued through the whole length of the cells, and as due to tubules.

1859. Lambl denied the presence of the rods, and considered the whole phenomenon an optical appearance due to the cell-wall; in this view he was supported by Vlakovich of Padua and Amici of Florence.

1860. Wiegandt held the border to be an independent covering, and the striation to be due to folding or wrinkling.

Col. Balogh described the border as formed of rods, but denied that these existed except when brought about by the action of fats; in support of this view he showed that the striation was wanting when fat was absent.

1865. Lipsky held the border to be composed of rods.

1866. Henle described the cells as in his former work, but now held the border to be composed of rods, in fact to represent a ciliated border.

1867. Erdmann described the border as being of two layers, an upper, thicker layer, with both longitudinal and transverse striation, and a lower, thinner layer, the true cell-wall. The upper layer he described as capable of splitting in the directions of both striations.

Schultze described the border as not being in intimate connection with the protoplasm of the cell. Arnstein and Wiegandt supported Heidenhain’s description.

1868. Albini e Renzoni described the part as resembling resting cilia.

1869. Eimer traced fat-globules into all the parts, epithelium, connective-tissue, and vessels; and held that the fat could pass from a lacteal to a branch of the Vena porta.

1870. Heidenhain, after further investigation, supported his earlier views.

1874. Thanhoffer described the membrane as perforated, and the protoplasm of the cells as actively sending protoplasmic processes through these apertures; this he had seen in frogs in which all connection with the spinal nerves had been severed.

1875. Benjamins could not find the striation to be a constant occurrence, and failed to find the processes described by Thanhoffer.

1876. Krause found rod-like bodies round the margin of the border.

1877. Fortunatow supported Thanhoffer’s view.

1881. Landois observed appearances in Spelerpes fuscus, which led him to support Thanhoffer’s views.

1883. Wiedersheim supported Thanhoffer’s views.

1884. Wiemer supported Thanhoffer’s observations.

1888. Paneth failed to find any contractile protoplasmic processes, and asserts that the circumference of the border, when examined under certain conditions, is composed of rods.

From the same causes the goblet- or chalice-cells, already mentioned, have been the subject of much speculation and investigation.

1846. Frerichs drew and described these cells as empty cells.

In 1848 these cells were first described as epithelium capitatum by Gruby and Delafond.

In 1856 Donders described the cells as being open, and as discharging their contents into the canal; the cell-walls being then pressed together by the neighbouring cells, and the cell-contents being then gradually reformed.

In the same year Kölliker published results closely agreeing with those of Donders, and he traced the various stages of the process.

1857. Brettauer and Steinach held them to be cells which had lost their contents, and as the ‘cuticular border’ was absent, concluded that the cell-contents were in closer connection with the ‘border’ than with the rest of the cell-wall.

1865. Lipsky and Sachs both doubted the presence of such cells, and considered them due to the action of reagents or post-mortem change.

1866. Letzerich described the cells as open, and regarded them as the commencement of the lacteal system, while Dönitz thought the whole appearance due to reagents.

1867. Schultze and Eimer, independently, described them as unicellular glands. Erdmann, however, again denied their occurrence under normal conditions.

Oeffinger held the goblet-cells to be modified ordinary cylindrical epithelium cells; in which view he was supported by Arnstein.

1868. Schultze and Eimer, after renewed investigations, reiterated their former opinions.

1869. Eimer described the goblet-cells as secreting mucin, and as capable, by division, of throwing out pus-like cells.

1876. Krause described the cells as containing granular contents, which under certain conditions are thrown out.

1877. Tolldt considered them artificial productions. Edinger asserted that they are formed from the cylindrical cells.

1877–1885. Partsch (1877), Klein and Hebold (1879), Stöhr (1880), Patzelt (1882), Haller (1883), Holl (1885), support the last view.

1878. Hoffmann supported Schultze’s views.

1886. List describes these organs as unicellular mucous glands.

1887. Paneth described them as secreting mucous and as being derived from the cylindrical cells.]

(5) [The *blood-vessels* of the small intestine (p. 234) have been described by Langer; he finds the vessels arranged in networks, one a subserous network, placed underneath the serous coat, and formed of elongated, irregular, four-cornered meshes. When the intestine is distended the meshes are rectangular.

The vessels to the mucous membrane divide and anastomose very freely in the submucous layer, and then form an irregular network on the inner surface of the _Muscularis mucosa_; this network follows all the foldings of the mucous membrane, and thereby supplies a double layer to each villous fold of the mucous membrane. The meshes are usually four-sided or five-sided.]

(6) [The *lymphatics* of the small intestine (Figs. 190, 191). The lymphatic vessels on reaching the intestine usually bifurcate; the two branches, as a rule, follow and enclose an arterial twig. From the serous layer they receive the contents of a very fine lymphatic plexus, the lumens of which are slightly greater than that of the corresponding capillaries; from the mucous layer they receive the contents of the lacteals: between these two layers the lymphatics anastomose very freely by means of numerous branches (Langer).

The lacteals are lined with an epithelioid layer and traversed by connective-tissue trabeculae, which have a like covering. The lacteals are not simple but in the form of a coarse network (Fig. 189) (Langer).]

[Illustration: Fig. 190.

Isolated fold of mucous membrane of small intestine of _Rana temporaria_; after Langer. Forty times natural size. Blood-vessels striped, lacteals shaded. ]

(7) [The *nerves* of the small intestine (p. 200) usually follow the arteries to the muscular coats, between which they form a plexus (Auerbach’s plexus); from this numerous twigs are given off, which course alone or in company with vessels to the mucous coat, where a second plexus (Meissner’s plexus) is formed. Auerbach’s plexus, according to Klein, consists of bands of nervous fibrils in endothelial sheaths; they branch and inosculate, and thus form a plexus. Where several such branches meet, a more or less complicated decussation of the bands of fibres takes place. Along these nervous bands are ganglion cells, either isolated or in groups. The cells are large, generally spherical, and contain a sharply outlined nucleus with a single or double nucleolus. The smaller cells generally appear to possess only one process, which can be traced from the protoplasm of the cell between the fibrils of the nerve-trunk. The larger cells are distinctly multipolar, their protoplasm being provided with a number of fine processes, or, as is oftener the case, with one large and several small processes. In many instances Klein was able to distinguish around the ganglion-cells a capsule of a spherical or ovoid shape. In these cases the body, as well as the processes of the ganglion-cell, were lying within the capsule. This system of ganglion-cells is in connection with the individual bundles within the nerve-trunks.

[Illustration: Fig. 191.

Transverse section of a fold of the mucous membrane of _Rana temporaria_; after Langer. Sixty times natural size.

_A_ Lacteals with transverse trabeculae. _B_ Circular muscular layer. _C_ Longitudinal muscular layer. Blood-vessels striped. ]

Klein describes a second system of ganglion-cells, situated in meshes, which are formed by the nerve-trunks of the plexus itself. These ganglion-cells are much larger than the former, and are multipolar; their protoplasm, which is distinctly fibrillar, with granules between the fibrils, is provided with one or two long, thick processes and several short and thin ones; generally the processes are branched. The general shape of the cells is oblong, the thick, long processes being commonly at the two opposite poles. The cells are generally isolated, sometimes situated in the centre of a mesh, or more commonly near a nerve-trunk that borders the mesh on one side. Each ganglion-cell is connected with a nerve-trunk of the plexus by at least one process. In a few of the nerve-trunks of the general plexus, isolated medullated nerve-fibrils are seen to pursue an almost straight course from one trunk into another and divide into two. There is no connection between these medullated fibres and the ganglion-cells.

*Auerbach’s plexus* is a much finer plexus than that just described, and the ganglia are much smaller. It supplies twigs to the _Muscularis mucosa_; these break up into fine fibrils, which follow the direction of the muscle-fibres; other twigs supply the blood-vessels, with which they can be traced into the bases of the folds of mucous membrane. Thanhoffer has recently (_l. c._) described nerve-fibrils, which terminate in the mucous epithelium.]

D. The _Large Intestine_ (Fig. 184 _R_).

[Illustration: Fig. 192.

From a transverse section of the large intestine of _Rana temporaria_, moderately distended.--G. H.

_A_ Denser portion of submucous coat. _B_ Looser portion of submucous coat. _C_ Artery, cut obliquely. _D_ Circular muscle-layer. _E_ Longitudinal muscle-layer. ]

*a.* *General description.* The large intestine is a flask-shaped viscus, lying in the median line. The small intestine opens into it by an abrupt curve at its anterior end. The large intestine is the widest part of the alimentary canal, is thin-walled, and diminishes in width towards its hinder end, where it opens into the cloaca above the opening of the bladder.

*b.* [*Minute structure.*

(1) The *serous coat* resembles that of the small intestine, etc.

(2) The *muscular coats* resemble those of the small intestine, but are thinner; the longitudinal layer is, however, proportionally thicker (Wiedersheim).

(3) The *submucous coat* (Fig. 192) resembles that of the small intestine in its general structure; the portion lying immediately beneath the mucous membrane (_B_) is denser in structure.

This layer has no _Muscularis mucosa_.

(4) The *mucous coat* (_A_) is a simple layer of large, columnar, epithelial cells, with large oval nuclei. The cells have a hyaline free border, but this possesses no striation. The mucous membrane is usually described as possessing numerous simple follicles (glands of Lieberkühn); in those specimens which I have examined they have been entirely absent (Figs. 192, 193). At six to eight points in a transverse section of a rectum moderately distended the submucous coat is thinner, and so throws the mucous coat into slight, longitudinal grooves; but these do not in the least resemble the glands of Lieberkühn.

[Illustration: Fig. 193.

Transverse section of large intestine of _Rana esculenta_; the mucous membrane thrown into longitudinal folds in consequence of the organ being contracted. Arteries injected with carmine.--G. H.

_A_ Large circular vessels within the muscular coats. _B_ Fine anastomosis to the mucous coat. ]

(5) The epithelium possesses goblet- or chalice-cells (Hoffmann), the number of which probably depends upon the period of the year and the state of digestion. In the rectum, from which the section for the figures 192 and 193 were cut, not one goblet-cell was found in a complete series of sections.

If the rectum be contracted, the mucous membrane is thrown into longitudinal folds.

(6) The *blood-vessels* (Fig. 193) have a simple arrangement. The arteries are large, and form oblique loops around the intestine, lying under the peritoneum; from these branches are given off to form a series of rings in the submucous membrane (Fig. 193 _A_); from these fine twigs are given off to form a fine anastomosis under the mucous membrane (_B_).

(7) The *lymphatics* of the large intestine are arranged in two chief systems: one under the serous coat resembles the corresponding system of the small intestine. The second set forms a network of rounded loops in the submucous coat, which give rise to a secondary set of smaller vessels towards the mucous membrane; this secondary system forms a sort of trellis-work standing on the rounded loops, and so maps out small blocks of the thick submucous coat. Towards the cloaca the arrangement is simpler; the secondary lymphatics are lost, while the primary lymphatics tend to form elongated, longitudinal loops (Langer).]

II. THE GLANDS CONNECTED WITH THE INTESTINAL CANAL.

A. The *Liver* and *Gall-bladder*.

*a.* *External form.*

(1) The liver (Figs. 185, 194) is a large, reddish-brown organ, occupying a large part of the anterior abdominal region. It consists of three or more lobes, which present many individual variations; as a rule there are two larger lateral lobes (_L_ and _L^1_), and a smaller median lobe (_L^2_). Each lobe has a superficial or ventral surface, which is convex, and a deep or dorsal surface, which is concave and directed towards the other abdominal viscera lying above the liver. The two surfaces of each lobe meet to form a sharp border around the lobe, except where the three lobes are more intimately attached, opposite the apex of the heart (Figs. 185, 194); at this place each lobe possesses a small, flat, or slightly concave anterior surface.

The left lobe (_L_) hides the greater portion of the stomach, and has near its inner border a deep fissure, which runs forwards and so marks off a more or less well-marked fourth lobe. The anterior portion of the left lobe is attached to the corresponding portion of the right lobe by a narrow commissure.

[Illustration: Fig. 194.

The liver, seen from the ventral surface.

_Du_ Duodenum. _H_ Heart. _L_ Left lobe of liver. _L^1_ Right lobe of liver. _L^2_ Middle lobe of liver. _M_ Stomach. ]

The median lobe (_L^2_) extends backwards as far as the pylorus, and covers the commencement of the intestine together with the pancreas; these organs can, therefore, not be seen until this lobe is displaced. A fifth lobe is sometimes found on the dorsal surface of the median lobe, and to it or to the dorsal surface of the median lobe the small intestine is attached by the _Ligamentum hepato-duodenale_ (Fig. 195 _Lhp_). The _Vena portarum_ enters the liver behind this ligament.

The right lobe extends much further dorsalwards than the left lobe, and even comes in contact with the lung, the vessels of which sometimes indent its surface in spirit specimens. This lobe is also in contact with the base of the fat-body, and in females with the oviduct.

By drawing the lobes of the liver to either side and displacing the heart towards the head, the posterior caval vein is seen passing from the liver to the heart, and the hepatic commissure joining the lateral lobes is brought into view.

(2) The *gall-bladder* (Fig. 195 _G_) is placed on the dorsal surface of the liver in the deep niche between the right and left lobes; it is attached to the liver by connective-tissue and peritoneum.

The gall-bladder is round or oval in form; when moderately full it has a smooth, outer wall, which is thin and allows the green colour of the bile to be seen. It possesses a duct (_Dcy_), the cystic duct (_Ductus cysticus_), which bifurcates near its origin.

The two cystic ducts (Fig. 195 _Dcy_) join the larger hepatic ducts, as shown in the figure, and so form a simple anastomosis, from which three branches (3) of varying size unite at the anterior extremity of the pancreas to form the common bile-duct (_Ductus choledochus_, _Dc_). The common bile-duct runs through the whole length of the pancreas, receiving near its origin additional hepatic ducts (_Dh^1_) from the middle lobe of the liver. In this course the duct lies either on the ventral surface of the pancreas or under a thin layer of the glandular tissue; it receives the ducts of the pancreas and leaves that organ at its posterior border as a round and strong canal (_Dc^1_). The duct courses in the gastro-duodenal ligament, and reaches the dorsal surface of the duodenum at a very acute angle; it then pierces the wall obliquely and terminates with a slit-like or elongated oval opening.

[Illustration: Fig. 195.

The pancreas and bile-canals. The liver has been displaced towards the head.

_Dc_ Common bile-duct. _Dc^1_ Common bile-duct after leaving the pancreas. _Dc^2_ Opening of the common bile-duct into the duodenum. _Dcy_ Cystic ducts. _Dh_ Hepatic ducts. _Dh^1_ Supplementary hepatic ducts from the middle lobe of the liver. _Du_ Duodenum. _G_ Gall-bladder. _L_ Left lobe of the liver. _L^1_ Right lobe of the liver. _L^2_ Middle lobe of the liver. _L^3_ Fourth lobe of the liver. _Lhp_ Gastro-hepatic ligament. _M_ Stomach. _P_ Pancreas. _Py_ Pylorus. _P^1_ Ducts of the pancreas. ]

*b.* [*Minute structure.*

(1) The *liver* is composed of various tissues: it possesses a peritoneal covering, a fibrous covering, which supplies trabeculae to support the various other tissues, blood-vessels, hepatic cells or true liver parenchyma, and bile-canals.

α. The *peritoneal covering* of the liver encloses the organ almost completely, the only exceptions being where the various attachments of the liver are found (see peritoneum). The peritoneal covering of the liver is for the most part composed of flattened, ciliated cells (Neumann and Grunau); on the middle lobe these are, however, more or less replaced by non-ciliated cells. The thickness of these cells varies considerably, according to the amount of distension to which the liver is subjected.

β. The *fibrous covering* of the liver is very thin and very difficult to demonstrate; it consists of connective-tissue fibres with very few corpuscles. This covering is prolonged into the liver along the portal canals, where traces of connective-tissue can always be made out.

From these processes and from the whole of the inner surface of the general connective-tissue capsule are given off fine trabeculae, in which it is very difficult to find any nuclei; these trabeculae are everywhere extremely delicate and difficult to demonstrate; nowhere do they form distinct boundaries between lobuli: the structure closely resembles the sustentacular tissue of a lymphatic gland (Eberth).

γ. The *blood-vessels* to the liver are the portal vessels (p. 249) the hepatic veins (p. 247), and the hepatic artery[74] (p. 233)

[Footnote 74: See Plate II, Fig. 196.

I. Partial injection of the liver from the portal vein (blue): _Rana esculenta_.--G. H.

II. Partial injection of the liver from the hepatic vein (red): _Rana esculenta_.--G. H.

III. Complete injection of the liver from the hepatic artery (red) and from the portal vein (blue): _Rana esculenta_.--G. H.

_A_ Portal (interlobular) veins and their branches. _B_ Hepatic (intralobular) veins and their branches. _C_ Hepatic arteries and their branches. ]

(1) The portal vessels pass into the liver on its ventral surface; they divide into branches which course along the middle parts of each lobe and give off smaller branches in all directions towards the periphery; the interlobular branches (Fig. 196 I) forming a very complex capillary network. As compared with the hepatic veins (Fig. 196 II), the interlobular veins do not give off their capillaries so abruptly, but tend to supply these from small lateral branches. The portal veins are accompanied in their course by branches of the hepatic artery, and often by larger bile-ducts, and thus form portal canals. In no part do the portal (interlobular) veins or their branches limit the lobules by distinct rings of vessels, as seen in many higher animals. The interlobular veins and intralobular veins simply interdigitate with each other.

(2) The hepatic veins (Fig. 196 I and II) also course chiefly in the middle parts of the lobes of the liver; they branch, and ultimately supply intralobular veins which interdigitate with the interlobular veins (I and II). The capillaries arise very abruptly from an intralobular vein, and form a network of vessels communicating very freely with the corresponding capillaries of the interlobular veins.

(3) The hepatic arteries (Fig. 196 III) break up into small branches which, as a rule, course along the portal canal until near the surface of the liver, when they leave the portal veins and pass to the surface to supply the coverings of the liver. In their course along the portal canals they supply a few very small twigs to the structures forming the canals. At the surface of the liver the branches of the hepatic artery form capillaries, which empty themselves into the general capillary anastomosis beneath (Fig. 196 III).

δ. The *liver-cells* (Figs. 197, 198) are large, and of compressed spheroidal or polygonal shape. They possess no cell-wall, have usually one but sometimes two large nuclei, each with a distinct nucleolus. The cells often contain granules of glycogen or fat-globules. The main fibrillae of the intercellular network are arranged so as to extend between a bile-capillary and a blood-capillary (Fig. 197).

ε. The *bile-ducts* (Fig. 198) commence as fine tubes between the liver-cells, where they are simply small spaces enclosed by the hepatic cells; they are usually enclosed by three or four cells, possibly sometimes by only two cells (Hering). Such bile-capillaries are usually separated from a blood-capillary by the thickness of one liver-cell only (Fig. 198).

As a number of such bile-capillaries run together to form a larger duct, the cells enclosing them change their character, becoming flattened and broader; these cells may, however, be traced continuously into the true hepatic cells (Hering and Eberth). The bile-duct so formed then obtains a slight covering of fibrous tissue, which rapidly increases in quantity, courses along a portal canal, and receives other ducts on the way; the epithelium lining it gradually becomes more elongated, and ultimately resembles that found in the common bile-duct or the gall-bladder.

In the larger ducts the epithelium is, according to v. Brunn, ciliated; they also possess a layer of unstriated muscle-fibre (Eberth).]

[Illustration: Fig. 197

Liver-cells, after Kupffer.]

ζ. The *pigment* of the liver varies very much in amount and character, according to the time of the year and state of health of the animal. According to Eberth the pigmentary masses are of about the same size as the white blood-corpuscles, and are possessed of the power of amoeboid movement (in young animals). The cells possess two to seven nuclei and vary much in colour and distribution. As a rule the larger the amount of pigment in a given liver the smaller is the number of fat-globules found in the individual liver-cells (Eberth).]

[Illustration: Fig. 198.

The bile-capillaries; natural injection with sulphindigotate of sodium: v v v represent blood-capillaries.--G. H.]

(2) [The *gall-bladder* and *bile-ducts*. The gall-bladder has four coverings.

α. A serous coat of peritoneal endothelium.

β. A muscular coat, containing unstriated muscle-fibres and connective-tissue.

γ. A sub-mucous coat of areolar-tissue.

δ. An internal lining of columnar epithelium.

ε. The walls of the gall-bladder are richly supplied with blood-vessels from the cystic arteries (p. 233); these form a close network in the submucous coat.

ζ. The muscular and submucous coats also possess a rich nervous plexus, which contains ganglia and resembles Auerbach’s plexus of the intestine (Popoff, Gerlach).]

B. The *Pancreas* (Fig. 199 _P_).

*a.* *General description.* The pancreas is a flattened, light yellowish-brown organ, placed in the loop of the duodenum between this latter and the stomach. The whole organ is within the gastro-duodenal ligament, and is attached to the liver; hence it is little influenced by changes in the amount of distension of the stomach or intestine.

[Illustration: Fig. 199.

The pancreas and bile-canals. The liver has been displaced towards the head.

_Dc_ Common bile-duct. _Dc^1_ Common bile-duct after leaving the pancreas. _Dc^2_ Opening of the common bile-duct into the duodenum. _Dcy_ Cystic ducts. _Dh_ Hepatic ducts. _Dh^1_ Supplementary hepatic ducts from the middle lobe of the liver. _Du_ Duodenum. _G_ Gall-bladder. _L_ Left lobe of the liver. _L^1_ Right lobe of the liver. _L^2_ Middle lobe of the liver. _L^3_ Fourth lobe of the liver. _Lhp_ Gastro-hepatic ligament. _M_ Stomach. _P_ Pancreas. _P^1_ Ducts of the pancreas. _Py_ Pylorus. ]

The organ may be completely exposed by either of two methods: in the former, the liver, stomach, and duodenum are drawn towards the head and the dorsal surface of the organ so exposed. In the second method the liver is drawn backwards, the various peritoneal folds which connect the duodenum with the posterior border of the liver cut through, and the three organs then separated; the pancreas can then be conveniently examined.

The size and shape of the pancreas are subject to great variations in different specimens. The usual shape of the organ is somewhat triangular (Fig. 199), the left border being usually unbroken, while the other two shorter borders are broken into lobes. The longest lobe stretches as far as the pylorus (_Py_), to which it is attached by connective-tissue: the opposite extremity of the gland is attached to the liver.

The excretory duct of the pancreas (_Ductus Wirsurgianus_) opens into the common bile-duct at about the middle of the pancreas (_P^1_); other smaller ducts may open into the same canal.

*b.* *Minute structure.* [The pancreas consists of a number of lobes loosely held together by connective-tissue; each lobe is composed of a number of lobules attached to each other much more intimately. The lobules are made up of tubes lined by a single layer of glandular epithelium. This epithelium is, as a rule, broadly columnar, but in the smaller tubes may be cubical or polygonal. Each cell has a cell-wall, nucleus, and very granular protoplasm; the latter shows two zones (in the inactive condition), a granular zone near the lumen, and an outer, clear, and finely striated zone (Nussbaum). The lumen of each alveolus is very small, and in many cases difficult to make out.

The smallest ducts have no special lining, and are therefore bounded by the glandular cells; the larger ducts have a flattened, cubical epithelium, which when seen from the surface has an appearance as if the individual cells were widely separated from one another; these ducts have a considerable layer of connective-tissue around them. The largest ducts are lined with a layer of columnar, ciliated epithelium; the cilia are very long, usually of about the same length as the cell, sometimes appearing to be even longer. This epithelium is continuous with the ciliated, epithelial layer of the common bile-duct, which it resembles. These largest ducts have an extremely thick layer of connective-tissue around them.

The pancreas and its ducts are very richly supplied with vessels and nerves; the nerves forming everywhere a fine plexus, the larger strands of which usually, but not always, course with the larger blood-vessels. The larger ducts have an especially rich supply of nerves, of which fibrils may be traced towards the ciliated epithelium; an anatomical connection between the two has not, however, been made out.]

III. THE SPLEEN.

*a.* *General description.* Although the spleen belongs to the lymphatic system, it is considered here in order to complete the description of the abdominal viscera. It is a small, rounded-oval body, of a reddish-brown colour, suspended in the mesentery near the anterior end of the large intestine (Fig. 184 _Mz_). In medium-sized animals the longer diameter is about 6 mm., and is parallel with the long axis of the body; the shorter diameter is about 5 mm., and the thickness varies from about 3 mm. to 4 mm. The dorsal surface is flat or slightly concave (_Hilus lienis_), and receives the relatively large afferent and efferent vessels; the rest of the organ is smooth and rounded, and with its greatest convexity directed towards the left side.

*b.* [*Minute structure.* The structure of the spleen resembles that of higher animals. It possesses a *serous coat* of peritoneum, under which is a *fibrous coat*; the latter sends in trabeculae, which divide and form a fine meshwork of supporting-tissue; the finest trabeculae are formed by the processes of the connective-cells of the sustentacular structure. According to Hoffmann, the thickness of the fibres averages 0.001 to 0.011 mm.; the intervening spaces measure 0.002 to 0.012 mm. The spaces are filled by the spleen pulp, which consists of true spleen-corpuscles, blood-corpuscles, and pigment-corpuscles.

The *spleen-corpuscles* have an average diameter of 0.006 mm., and are round or of a rounded oval form. Each consists of a nucleus, with a very small amount of adherent protoplasm; the nucleus possesses one or two nucleoli. Some of these cells contain a brownish or black pigment in granules, but most of them are colourless (Hoffmann).

The *pigment-cells* equal the white blood-corpuscles in size, and exactly resemble the corresponding pigment-cells of the liver.

The *blood-corpuscles* are found in various stages of disintegration and regeneration.

The *arteries*, on entering the spleen, at once break up into branches which pass in all directions, giving off twigs on all sides and at varying angles; from these capillaries are supplied, which traverse the parenchyma in all directions. The capillaries empty themselves partly into veins, partly into the splenic spaces.

The *veins* commence either as capillaries in connection with the arteries or by communicating with the splenic spaces. This communication is brought about by small twigs of about 0.015 mm. diameter, which have incomplete walls, and so open into the splenic spaces (Hoffmann).

*Malpighian bodies* are represented by collections of splenic cells on various arterial twigs; they are, however, not so sharply defined as is the case in some higher animals.]

IV. THE PERITONEUM.

*a.* *General description.* The *peritoneum* is a thin, pigmented membrane lining the abdominal cavity. Tracing it forwards from the ventral wall of the abdomen (_Peritoneum parietale_), it can be followed along the deeper surface of the muscles to the pericardium. The middle portion leaves the abdominal wall by accompanying the anterior abdominal vein; the lateral portions are continued further forwards, and then ascend on the pericardium and the deeper surfaces of the lateral walls in the thoracic region.

The peritoneum passes thence to the ventral surface of the liver (_Ligamentum coronarium_), covers this surface and passes on to the dorsal surface of the organ, which, together with the gall-bladder, it completely encloses. The membrane thus reaches the dorsal wall (_Ligamentum suspensorium hepatis et pericardii_); from the lateral borders of the liver it passes upwards to the dorsal wall, and thus forms a pocket-like pleuro-peritoneal cavity on either side.

From the dorsal wall and above the attachment of the coronary ligament of the bladder the peritoneum reaches the root of the lung on each side, and completely invests the organ: while in the middle line it covers the outer surface of the oesophagus and attaches it to the dorsal wall, thus forming the first part of the mesentery.

Just behind the root of the lung, the peritoneum, in female specimens, has an opening on each side (_Ostium abdominale tubae Fallopiae_), by which the oviduct communicates with the peritoneal cavity.

Tracing the peritoneum backwards, it passes over the ventral surface of the kidneys so as to exclude them from the peritoneal sac: in the middle line, between the kidneys, the peritoneum descends to form the mesentery for the small intestine. At the inner borders of the kidneys, the testes or ovaries are pushed into the abdominal sac, and so possess well-marked mesenteries; the mesovarium becomes longer towards the cloaca, but attains its greatest development in the breeding season, when it is arranged in numerous folds. Along the outer borders of the kidneys, in females, the peritoneum again descends into the abdominal cavities to enclose the oviducts, which have broad mesenteries. Towards the rectum these mesenteries are shorter and attached to either side of the bladder by a well-marked free border: as the middle line of the bladder is attached by the peritoneum to the rectum, two distinct pouches (_Cava recto-vesicalia_) are formed, which descend deeply into the pelvic cavity. The upper walls of these pouches are pushed in between the urostyle and the rectum, and together form a strong meso-rectum, which is longer near the _Valvula Bauhinii_ and continuous with the mesentery of the small intestine. The hinder portion of this mesentery is very short, and only covers the lateral walls of the rectum.

With the exception of a small portion of its dorsal surface, which is attached to the rectum, the whole surface of the bladder is covered with peritoneum.

The mesentery of the alimentary canal commences in connection with the oesophagus between the roots of the lungs; it is attached to the dorsal surface of the liver, covering the posterior caval vein, and is attached to the gall-bladder. From this point it extends, as a free, arched fold, to the concave right border of the stomach, which is completely surrounded by peritoneum.

The gastro-duodenal fold (_Ligamentum gastro-duodenale_) extends from the stomach to the pylorus and includes the pancreas. The hepato-duodenal fold (_Lig. hepato-duodenale_) extends from the portal fissure of the liver to the duodenum.

The mesentery of the small intestine is broad and arranged in folds, which follow the curves of the intestine; and is attached in the middle line, immediately beneath the vertebrae, where it encloses the aorta.

The various folds and mesenteries carry the blood-vessels and nerves to the different organs; in this course the vessels are surrounded by large lymphatics, which communicate with each other.

[Illustration: Fig. 201.

Preparations from the peritoneum of _Rana esculenta_.--G. H.

I. From peritoneum of the ventral wall of abdomen, stained with silver and logwood (Hartnack, Oc. I, Syst. 7).

II. From mesentery of small intestine of _Rana esculenta_, stained with silver (Hartnack, Oc. I, Syst. 7).

III. Preparation to show ciliated cells between non-ciliated cells; after Neumann. IV. Vertical section at border of liver to show ciliated epithelium; after Neumann.

_A_ Stoma. _B_ Pigment-cells. _C_ Ciliated cells. _D_ Non-ciliated cells. ]

*b.* *Minute structure* (Fig. 201).

[The peritoneum is a serous membrane, formed for the most part of a layer of irregular endothelial cells, arranged on a thin layer of subserous, connective-tissue (Fig. 201 I, II, and III).

The endothelial cells are attached to each other by cement-substance, easily stained by silver nitrate. The cells covering the general surface of the peritoneal cavity are larger and broader than those covering the mesentery of the small intestine (compare I and II, Fig. 201).

At various points stomata are found, bordered by smaller and more deeply staining epithelium (I, _A_). The membrane covering the general cavity is also much more pigmented than that covering the mesentery (compare I and II).

Various portions of the peritoneal surface possess ciliated cells, and these cells are usually thicker than the surrounding non-ciliated cells. Such cells are found especially near the openings of the oviducts and on the liver. The dimensions of the cells vary; according to Neumann the average dimensions of ciliated cells on the liver are: 0.006 mm. depth (without the cilia); nucleus, 0.012 mm. long and 0.003 mm. broad. The cells are five- or six-sided and bounded by straight sides (Neumann).]

SECTION VI.

THE LARYNX, LUNGS, VOCAL SACS, THYMUS AND THYROID GLANDS, AND THE LYMPHATIC GLANDS (TONSILS?) OF THE HYOID REGION.

THE LARYNX, LUNGS, VOCAL SACS, ETC.

LITERATURE.

THE LUNGS AND LARYNX.

*Arnold, J.*, Zur Histologie der Lungen des Frosches. Virchow’s Arch. 1863. Vol. XXVIII, p. 433.

*Auerbach, L.*, Ueber den Bau der Blutcapillaren in den Lungen des Frosches und an einigen andern Orten. Amtlicher Bericht über die vierzigste Versammlung deutscher Naturforscher und Aerzte. 1886, p. 241.

*Brittan*, Brit. and Foreign Medico-chirurgical Review, 1857. Vol. XX.

*Eberth, C. J.*, Ueber den feineren Bau der Lunge. Zeitschr. f. wiss. Zool. 1863. Vol. XII, p. 427.

*Eberth, C. J.*, Ueber den Bau und die Entwicklung der Blutcapillaren. Würzburger naturw. Zeit. 1866–67. Vol. VI, pp. 27–32.

*Egorow, W.*, Ueber die Nerven der Lungen. Centralbl. f. med. Wiss. 1879, p. 305.

*Elenz, E.*, Ueber das Lungenepithel. Würzburger naturw. Zeit. 1864. Vol. V, pp. 66–84.

*Frommann, C.*, Ueber die spontan, wie durch Durchleiten inducirter Ströme, an den Blutzellen v. Salamandra maculata und an den Flimmerzellen von der Rachen-schleimhaut des Frosches eintretenden Veränderungen. Jenaische Sitzungsb. 1880.

*Gegenbaur, C.*, Ueber Drüsenzellen in der Lungen-Schleimhaut bei Amphibien. Arch. f. Anat. u. Physiol. 1863, p. 157.

*Griffini, L.*, Contribuzione alla patol. del tessuto epiteliale cilindrico. Arch. per le scienze mediche, 1884. Vol. VIII, pp. 1–43.

*Grützner*, Physiologie der Stimme und Sprache. Hermann’s Handb. d. Physiol. Vol. I, Pt. II, p. 146.

*Henle, J.*, Vergleichende Anatomische Beschreibung des Kehlkopfes. Leipzig, 1839.

*Hoffmann, C. K.*, in Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig und Heidelberg, 1873–78. Vol. VI, pp. 514–531.

*Hoffmann, T.*, Die Lungengefasse der Rana temporaria. Dissert. Dorpat, 1875.

*Holmgren, F.*, Upsala Läkareförenings Förhandlingar, 1867. Vol. III, pp. 389–399.

*Howes, G. B.*, On a hitherto unrecognised feature in the larynx of the anurous amphibia. Proc. Zool. Soc. London, 1887, p. 491.

*Hüter, C.*, Ueber den Kreislauf und die Kreislaufsstörungen in der Froschlunge. Centralbl. f. med. Wiss. 1873. Nos. 5 and 6.

*Kandarazki, M.*, Ueber die Nerven der Respirationswege. Arch. f. Anat. u. Phys. 1881, p. 1.

*Küttner*, Beitrag zu den Kreislaufsverhältnissen in der Froschlunge. Virchow’s Arch. 1874. Vol. LXI, p. 21.

*Leydig*, Anatomische-histologische Untersuchungen über Fische und Reptilien. 1853.

*Malpighi*, De pulmonibus. Oper. omn. Lugd. Batav. 1687. Vol. II, p. 328.

*Müller, H.*, Ueber das Vorkommen glatter Muskelfasern in den Lungen der Amphibien. Würzburger naturw. Zeit. 1861.

*Pertik, O.*, Untersuchungen über Nervenfasern. Arch. f. mik. Anat. 1881. Vol. XIX, p. 183.

*Ranvier, L.*, Leçons sur l’histologie du système nerveux. Vol. I, pp. 98–101.

*Schestopol, A.*, Ueber die Durchlässigkeit der Froschlunge für gelöste und körnige Farbstoffe. Virchow’s Arch. 1879. Vol. LXXV, p. 199.

*Schultze, F. E.*, Epithel und Drüsenzellen. Arch. f. mik. Anat. 1867. Vol. III, p. 145.

*Schultze, F. E.*, Die Lungen, in Stricker’s Handbuch der Gewebelehre.

*Stirling, W.*, On the nerves of the lungs of the newt. Journ. of Anat. and Physiol. 1882, p. 96.

*Treviranus, C. R.*, Beobachtungen aus der Zootomie u. Physiologie; nach dessen Tode herausgegeben von L. C. Treviranus. Bremen, 1839.

THE THYMUS GLAND.

*Ecker*, Blutgefässdrüsen, in Wagner’s Handwörterbuch der Physiologie, 1853. Vol. IV, p. 114.

*Fleisch, E.*, Ueber den Bau einiger sogenannten Drüsen ohne Ausführungsgänge. Wiener Akad. Sitzungsb. 1870. Vol. LX, Pt. II, p. 55.

*Gegenbaur*, Vergleichende Anatomie.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreiches. 1873–1878. Vol. VI, p. 503.

*Leydig*, Lehrbuch der Histologie. 1857, p. 422.

*Tolldt*, Ueber lymphoide Organe der Amphibien. Wiener Acad. Sitzungsb. 1868. Vol. LVIII, Pt. II, p. 171.

*Watney, H.*, The minute anatomy of the thymus. Phil. Trans. 1882. Vol. CLXXIII, p. 1100.

THE THYROID GLAND.

*Baber, E. C.*, Researches on the minute anatomy of the thyroid gland. Phil. Trans. 1881. Pt. III, p. 577.

*Ecker*, Blutgefässdrüsen, in Wagner’s Handwörterbuch der Physiologie, 1853. Vol. IV.

*Fleisch, E.*, Ueber den Bau der sogenannten Schilddrüse des Frosches. Wiener Acad. Sitzungsb. 1868. Vol. LVIII, p. 57.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreiches. 1873–1878. Vol. VI, p. 503.

*Huxley* and *Martin*, Practical Biology. 4th edit., 1877, p. 181.

*Leydig*, Lehrbuch der Histologie. 1857, p. 376.

*Müller, J.*, Ueber die Entwicklung der Schilddrüsen des Frosches. Wiener Sitzungsb. 1871. Vol. VI, pp. 428–553.

*Müller, W.*, Ueber die Entwicklung der Schilddrüse. Jenaische Zeitschr. 1871. Vol. VI, p. 438.

*Poincaré*, Zur Anatomie der Glandula thyroidea. Journ. de l’anat. et de la physiol. 1877. Vol. XIII, pp. 123–143.

*Rolleston*, Forms of Animal Life. 2nd Edit. 1888, p. 77.

*Zeiss, O.*, Mikroskopische Untersuchungen über den Bau der Schilddrüse. Dissert. Strassburg, 1877.

THE LARYNX, LUNGS, VOCAL SACS, ETC.

I. THE LARYNX.

The larynx (Fig. 202) is a short wide tube placed between the posterior cornua of the hyoid, to which it is attached by connective-tissue. The long axis of the tube lies in the median line and almost horizontally, but the posterior end is on a slightly lower level than the anterior, when the animal is in the natural sitting position (Fig. 202). The anterior end of the larynx opens into the mouth by a longitudinal slit (Fig. 179 _L_), and is placed in a slight depression caused by the folding of the mucous membrane; the posterior end communicates with the cavities of the lungs.

[Illustration: Fig. 202.

Dissection to show the position and relations of the larynx. The animal (_Rana esculenta_) is in the natural sitting position; the toes of the fore-foot are, however, too much flexed.--G. H.

_B_ Brain. _C_ Gall-bladder. _E_ Opening of Eustachian tube. _Eo_ Oesophagus. _F_ False vocal cords. _G_ Epiglottis. _H_ Heart. _L_ Liver. _V_ True vocal cords. ]

The larynx is lined with mucous membrane, which is continuous, in front with that of the mouth, behind with that of the lungs. The organ has a skeleton of cartilage, and possesses special muscles, by which the supply of air to the lungs, and the voice can be regulated.

*a.* The *cartilages* of the *larynx*.

The cartilages of the larynx are five in number, of which four are paired and one is single.

(I) The *cricoid cartilage* (Figs. 203, 204) is an oval ring of cartilage with various processes. The ring-like portion of the cartilage is placed in a plane which is almost vertical, but which is directed slightly upwards anteriorly, and slightly downwards posteriorly (the animal being in the usual sitting position).

[Illustration: Fig. 203.

The cartilaginous skeleton of the larynx.

I. Seen from in front; the spinous process would normally be more curved.

II. Seen from the left side; the spinous process should be more curved.

_Ca_ Right arytenoid cartilage. _Ca^1_ Left arytenoid cartilage. _C.l.^1_-_C.l.^4_ Cricoid cartilage. _P_ Lateral plate of cricoid cartilage. _Sp_ Spine of cricoid cartilage. _SR_ Opening to larynx. *** The two outer asterisks are above the two apices of the left arytenoid cartilage; the middle one above the pre-arytenoid cartilage. ]

The sides of the ring are slightly curved inwards on the anterior surface, and possessed of irregular enlargements (_C.l.^1_-_C.l.^4_), the space enclosed by this portion of the cartilage is occupied by a membrane (_M_), which forms the floor of the body of the larynx.

From each side of the body of the cartilage, a process (_C.l.^2_) is given off, which curves backwards and inwards to join its fellow of the opposite side, the two forming a blunt spinous process (_Sp_), which projects backwards, and is intimately attached to the oesophagus. Between these processes and the lower portion of the body of the cricoid cartilage are the apertures of the roots of the lungs (Fig. 203), which, by their attachments to these cartilages, are kept open.

(2) The *arytenoid cartilages* (Fig. 203 I, II, _Ca_, _Ca^1_) are a pair of cartilages placed in front of the cricoid cartilage, one on each side. Each cartilage is semilunar in shape, concave internally, and convex externally. The cartilages are placed almost vertically, with their posterior borders or bases parallel to the body of the cricoid cartilage. The superior borders (Fig. 204) are directed upwards and forwards, the inferior downwards and forwards. The superior and inferior borders are separated by a semicircular notch, bounded by two sharp apices. The superior and inferior angles of the two cartilages are close together, and movably attached to each other by connective-tissue.

These cartilages vary very greatly in the two sexes. In the males they are thick, strong, and large; in the female the cartilages are very thin, more hollowed and much smaller.

[Illustration: Fig. 204.

The larynx and surrounding parts, seen from the ventral surface.

_Ca^1_ Arytenoid cartilages. _Cl^1_-_Cl^4_ Cricoid cartilage. _G_, _G^1_ Fibrous tissue connecting the larynx with the posterior cornua of the hyoid. _H_ Lesser cornua of the hyoid. _HH_ Greater cornua of the hyoid. _Lg_ Right lung. _Lg^1_ Left lung. _M_ Fibrous membrane filling the ring-like cricoid cartilage. _Ph^4_ The M. petrohyoideus tertius. _S_ Part of tendon of M. petrohyoideus tertius. _SB_, _SB^1_ Mucous membrane bulging from the anterior ventricle of the larynx. _Sp_ Spinous process of the cricoid cartilage. _ZK_ Body of the hyoid. ]

(3) [The *pre-arytenoid cartilages* (Fig. 206 I, _P_) are two small elongated cartilages placed in the semicircular notch between the superior and inferior borders of the arytenoid cartilages. They are subject to much variation in size, sometimes being merely a very slender rod, at others a moderately thick oval mass. In female specimens they appear to be, at times, absent, or to unite with the arytenoid cartilages, as in these cases a third very small apex is found on each arytenoid cartilage; but it is always much smaller than the two neighbouring apices.]

*b.* The *attachments* of the *cartilages* to each other.

The cartilages do not articulate directly with each other, but are connected by connective-tissue only; there are, therefore, no synovial sacs.

[Illustration: Fig. 205.

The muscles of the larynx.

_A.l._ Aperture between the arytenoid cartilages. _C.l._ Cricoid cartilage. _C.a.^1_ Superior angle of the arytenoid cartilage. _C.a.l._ M. constrictor aditus laryngis. _C.o.l._ M. hyo-arytenoideus anterior. _C.o.l.^1_ M. hyo-arytenoideus posterior. _D.l._ M. dilatator laryngis. _G_ Connective-tissue. _G^1_ Connective-tissue. _H_ Smaller posterior cornua of the hyoid. _HH_ Greater cornua of the hyoid. _Jt_ Fibrous tissue into which the two constrictions are inserted. _Ph^2_ Second petrohyoid muscle (M. petrohyoid. I). _Ph^3_ Third petrohyoid muscle (M. petrohyoid. II). _Ph^4_ Fourth petrohyoid muscle (M. petrohyoid. III). _S_, _S^1_, _S^2_ Tendon of the fourqth petrohyoid muscle. _Sp_ Spinous process of the cricoid cartilage. _ZK_ Body of the hyoid. ]

*c.* The *muscles* of the larynx[75].

[Footnote 75: The nomenclature adopted is that of Henle and Hoffmann.]

The muscles of the larynx appear in the following order, when dissected from the mouth:--

(1) The _M. dilatator aditus laryngis_ (Henle), (Fig. 205 _D.l._) arises on either side from the hinder end of the larger posterior cornu of the hyoid: the fibres diverge slightly to be inserted into the middle portion of the outer surface of the arytenoid cartilage; a smaller bundle of fibres is attached to the deeper-lying constrictor muscle and to the cricoid cartilage.

(2) The _M. constrictor aditus laryngis_ (Henle), (Fig. 205 _C.a.l._), arises on either side from the hinder half of the dorsal surface of the posterior cornu of the hyoid. The two muscles enclose the larynx, and are inserted into a median tendinous raphe on the under surface of the larynx (_Jt_). The raphe is connected with the skeleton of the larynx by connective-tissue.

(3) The _M. hyo-arytenoideus anterior_ (Fig. 205 _C.o.l._) arises on each side from the inner border of the anterior end of the cornu of the hyoid; the muscle lies close to the anterior border of the arytenoid cartilage, and is inserted into a fibrous lamella on the dorsal surface of the larynx. The _M. petrohyoideus tertius_ is also partially inserted into this lamella.

(4) The _M. petrohyoideus tertius_ (Fig. 205 _Ph^4_), (see also p. 66). The greater part of this muscle is inserted into the end of the posterior cornu of the hyoid (_HH_); a smaller portion (_S_, _S^2_) is prolonged to be inserted into the cricoid cartilage and into the fibrous lamella into which the _MM. hyo-arytenoidei anteriores_ are inserted.

(5) The _M. hyo-arytenoideus posterior_ (Fig. 205 _C.o.l.^1_) arises on each side from the superior angle of the corresponding arytenoid cartilage, under cover of the tendon of the _M. petrohyoideus tertius_. The muscle is inserted into the inferior angle of the arytenoid cartilage.

*d.* The *interior* of the larynx (Figs. 202, 206, 207). The cavity of the larynx is constricted at two points: anteriorly it is constricted by the true vocal cords (Figs. 206 _V_, 207 _SB_), posteriorly by the false vocal cords. The whole cavity is lined with mucous membrane, which is continuous with that of the mouth anteriorly, with that of the lungs posteriorly.

(1) The *true vocal cords* are two vertical flat bands of connective-tissue, attached above to the superior angles of the arytenoid cartilages, below to their inferior angles; their anterior borders are thin and free; near their posterior borders they are attached by mucous membrane to the internal surfaces of the arytenoid cartilages. The anterior and posterior borders are not parallel but are each concave (Fig. 202 _V_).

[Illustration: Fig. 206.

Three sections through the larynx of _Rana esculenta_.--G. H.

I. Sagittal section near the median plane through the larynx.

II. Oblique transverse section through larynx.

III. Almost horizontal section through larynx.

_A_ Arytenoid cartilage. _C_ Cricoid cartilage. _E_ Epiglottis. _F_ False vocal cords. _G_ Epiglotidean glands. _H_ Hyoid. _M_ Membranous floor of the larynx, cut obliquely. _O_ Opening into root of lung. _P_ Pre-arytenoid cartilage. _V_ Vocal cord. ]

The anterior border is thin, the posterior thick and rounded.

Seen from in front (Fig. 206), the opening between the cords (_Rima glottidis_) is slightly wider at each end than in the middle. The ends of the concave posterior border are prolonged backwards and enclosed in a fold of mucous membrane. Part of the tissue enclosed is unstriated muscular fibre, which may be traced to the cricoid cartilage.

(2) [The *false vocal cords* (Figs. 202 and 206 _F_) are simply folds of mucous membrane, which extend vertically on each side of the larynx behind the true vocal cords; they do not extend so far towards the median plane as do the true vocal cords.]

(3) [The *ventricles* of the larynx (Figs. 202 and 206) are two on each side. The anterior ventricles are between the true vocal cords and the arytenoid cartilages; they are open anteriorly, and closed by mucous membrane posteriorly.

The posterior ventricles open towards the median plane, each presenting an oval opening (Fig. 202), which widens outwards into a large cavity (Fig. 206 _II_). The cavity is bounded in front by the base of the true vocal cord, and the mucous membrane attached to it; posteriorly by the false vocal cord, and externally by the cricoid cartilage and the connective-tissue capsule of the larynx.]

(4) [The *mucous membrane* of the larynx varies in structure in various parts of the organ. From the anterior opening of the larynx to the posterior borders of the vocal cords it is lined with stratified epithelium, which is firmly attached to the underlying structures by a small amount of sub-epithelial tissue. This is especially well marked on the vocal cords themselves.

Behind the vocal cords the mucous membrane is much more loosely attached to the surrounding structures by an extremely vascular areolar tissue. The epithelium is arranged in a single layer of columnar cells, among which are numerous goblet-cells. In the more external parts of the posterior ventricles, the mucous membrane is thrown into deep folds and so forms polygonal acini. In the median line of the floor of the larynx and behind the false vocal cords is a vertical fold of mucous membrane, which increases in height and breadth as it proceeds backwards towards the roots of the lungs. The mucous membrane behind the true vocal cords is extremely vascular, in the most posterior portion of the larynx the blood-vessels form a capillary network exactly like that of the lungs.]

*e.* [The *epiglottis* (Fig. 206 _E_) is a small bilobed fold of mucous membrane placed on the floor of the mouth in the median plane and immediately in front of the aperture to the larynx. Between it and the mucous membrane covering the arytenoid cartilages are a number of large mucous glands (_G_). The epiglottis does not contain cartilage; it is, however, constant in its appearance and sharply marked off from the surrounding mucous membrane.]

II. THE LUNGS.

*a.* *General description.* The lungs are two large thin-walled sacs (Figs. 185 and 204 _Lg_ and _Lg^1_). The roots of the lungs are contracted at their origin from the larynx and then expand to form two ellipsoid sacs, which terminate posteriorly in bluntly-pointed ends. With the exception of their roots they lie entirely free in the pleuro-peritoneal cavity, and are covered by the pleuro-peritoneal membrane. In the recent state they have a bright red colour due to the large supply of blood-vessels.

[Illustration: Fig. 207.

The Rima glottidis, seen from the front.

_G_ Rima glottidis. _SB_ Vocal cords. ]

*b.* *Minute structure.*

(I) The *muscular tissue* of the lungs is for the most part arranged in large bands, which form a coarse network on the deeper surface of the organ; when seen in section[76] (Pl. II, Fig. 208 _A_, _B_) these bands are found to be composed of well-developed involuntary muscular fibres. Between the larger bands are smaller bands having a similar arrangement. From these networks of muscular bands finer processes of muscular tissue pass peripherally towards the surface of the organ, and are attached to the thin and incomplete muscular layer found in the wall of the lung (_C_).

[Footnote 76: See Plate II, Fig. 208.

Two sections from the lung of _Rana temporaria_; stained with borax carmine.--G. H.

I. The lung dilated (Hartnack, Oc. I, Syst. 3). II. The lung contracted (Hartnack, Oc. I, Syst. 7).

_A_ Band of muscle cut transversely. _B_ Band of muscle cut longitudinally. _C_ Muscular layer of surface. ]

(2) The *connective-tissue* of the lungs is present in only small quantity, but is still sufficient to fill in the spaces between the various muscular bands and the surface of the lung, and to invest the whole of that surface. There is thus formed a series of pits, the mouths of which open into the general cavity of the lung, while their bases are at the surface. Through this connective-tissue course the blood-vessels, nerves, and lymphatics. It contains numerous yellow elastic fibres.

(3) The *blood-vessels* of the lungs. The pulmonary artery courses along the outer surface of the lung to the apex, giving off, at right angles, lateral branches in the whole of its course; these show a tendency to be alternately larger and smaller. The lateral branches divide and form a rich capillary network (T. Hoffmann).

The capillary network has very small meshes; the diameter of a given mesh being frequently less than that of the capillary bounding it. The meshes are rounded or polygonal in shape.

The pulmonary vein arises by lateral branches from this capillary network; the branches join, at right angles, the main vein, which courses from the apex of the lung along its inner surface to the root of the organ.

(4) The *epithelium* of the lungs. Externally the lungs are covered with a layer of endothelium derived from the peritoneum. Internally the surface is covered with an epithelium which varies considerably in different positions.

On the free borders of the muscular trabeculae forming the borders of the alveoli is a short columnar ciliated epithelium (Fig. 208) such epithelium is also found in the root of the lung; it contains goblet-cells.

The alveoli, for the most part, are lined with a single layer of tesselated epithelium; the cells are polygonal in outline, with finely granular contents and a distinct nucleus: the average diameter of the cells is from 0.0074 to 0.0108 mm., that of the nucleus 0.0054 mm., that of the nucleolus 0.0009 mm.; four to eight of such cells occupy the space enclosed by one mesh of the capillary network (Eberth).

The epithelium rests on a structureless basement membrane, which is continuous over the whole inner surface of the lung, whereas the epithelium does not pass over the capillaries, and is therefore only found in isolated patches in the areas enclosed by the capillaries (Eberth).

In various isolated spots, small groups of short columnar or goblet-cells are found in the tesselated epithelium (Eberth, Hoffmann).

(5) [The *lymphatics* of the lungs have been described by T. Hoffmann; they form a network of vessels surrounding the larger blood-vessels: from this branches are given off, which form a network of fine canals through the whole of the lung; part of this secondary network accompanies the blood-capillaries, but other portions run a separate course. They communicate with the pleuro-peritoneal cavity.

(6) The *pigment-cells* are very numerous, branched, and large; they accompany the lymphatics, and not the blood-vessels (T. Hoffmann).

(7) The *nerves* of the lungs (p. 172) course along the larger blood-vessels, under the serous coat; the fibres are chiefly medullated fibres (Egorow, Kandarazki). Non-medullated branches, which form a plexus in each alveolus, are given off. The branches have small triangular enlargements (ganglia), where they unite. The nerves are accompanied by nerve-cells, which occur either singly or in groups.

Egorow describes the nerves as being distributed in three networks: one for the mucous membrane and muscular trabeculae; a second for the superficial muscular layer; and a third for the serous membrane.]

III. THE VOCAL SACS.

*a.* *General description.* The vocal sacs are a pair of sacs which open in the floor of the mouth (Fig. 179 _S_); they are found only in the males. When the animal croaks these sacs are dilated and act as resonators; when so dilated the sacs force up the skin under the angle of the mouth and tympanic membrane. In well-developed specimens they are about as large as an average sized cherry. The skin covering the sacs is extremely elastic, but is not directly attached to the sacs.

*b.* *Minute structure.* The sac consists of connective-tissue, with a large proportion of yellow elastic fibre. Internally it is lined with a flattened epithelium, and externally is covered with a layer of striated muscular fibre, derived from the mylo-hyoid muscle (Fig. 209 _My_, _My^1_).

IV. THE THYMUS GLAND.

*a.* *General description.* The thymus gland (Fig. 210 _Th_) is placed on each side behind the angle of the jaw; it is best exposed by removing the skin behind the tympanic membrane and the angle of the jaw, and then reflecting the _M. depressor mandibulae_ (_D.m._). The gland is then found as an elongated, oval body, not quite 3 mm. long, lying in the space between the _M. depressor mandibulae_ and the _M. sternocleidomastoideus_ (_St_); it extends slightly beyond the posterior border of the former muscle. The space also includes connective-tissue, fat, and numerous vessels.

In _Rana temporaria_ this gland is spherical, much smaller, and placed further behind on the _M. sternocleidomastoideus_, between the _M. latissimus dorsi_ and the _M. deltoideus_ (Wiedersheim).

[Illustration: Fig. 209.

Dissection to show the vocal sac of the right side.

_HH_ Larger posterior cornua of the hyoid. _HH^1_ Smaller posterior cornua of the hyoid. _My_ Mylo-hyoid muscle. _My^1_ Mylo-hyoid muscle continued on to the vocal sac. _Thy_ Thyroid glands. _VH_ Anterior cornua of the hyoid. _Z_ Body of the hyoid. ]

*b.* *Minute structure* (Fig. 211).

[The gland is surrounded by a connective capsule, which is indented on the inner surface to form a hilus through which blood-vessels course into the organ.

The capsule sends in numerous fine trabeculae, which form a connective-tissue skeleton such as is found in all lymphatic glands. The corpuscles of the trabeculae possess elongated nuclei from 0.019 to 0.028 mm. in length, and 0.010 to 0.015 mm. in breadth (Tolldt). The trabeculae support a network of blood-vessels.

The meshes of this sustentacular tissue are filled with *cells*; these are:

(α) Lymphoid cells, rounded or oval, possessing a round nucleus and nucleolus, and an extremely small amount of adhering protoplasm; the size of the nucleus is from 0.011 to 0.015 mm. (Tolldt).

[Illustration: Fig. 210.

Dissection to show relations of the thymus gland.

_De._ M. deltoideus. _D.m._ M. depressor mandibulae. _L.d._ M. latissimus dorsi. _St_ M. sternocleidomastoideus. _Tf_ Tympanic membrane. _Th_ Thymus gland. ]

[Illustration: Fig. 211.

From various sections from the thymus gland of _Rana esculenta_.--G. H.

I. Complete gland (Hartnack, Oc. I, Syst. 3).

_a_ Pigment-cells.

II. Portion of a section (Hartnack, Oc. I, Syst. 7) showing small corpuscles of Hassall.

III. Portion of a section showing lobules with degenerating cells.

_a_ Capsule of lobe. _b_ Lobules. _c_ Large corpuscle of Hassall, surrounded by normal tissue.

IV. Nerve-cell? (corpuscle of Hassall), after Fleischl. ]

(β) Corpuscles of Hassall (Fig. 211 II, III, and IV) are, as a rule, large bodies, but are subject to much variation in size. Their general appearance is seen in Fig. 211 III; they show a concentric striation and usually enclose one or more smaller cells. They therefore closely resemble similar corpuscles found in higher animals.

(γ) In many frogs the cellular structure of at least a part of the gland seems to have undergone a degenerative stage (III). In such cases the connective-tissue is increased in quantity, and marks off portions of the section into small lobules (III) which are filled with cells containing mucus or sometimes fat (III). Under what conditions this degeneration, if such it be, takes place has not yet been determined[77].

[Footnote 77: Only winter-frogs were at my disposal (translator).]

(δ) Large branched pigment-cells are found in the course of the larger blood-vessels.

(ε) Watney describes also four varieties of ‘granular cells:’ 1. polygonal or rounded; 2. vacuolated; 3. spheroidal masses; 4. club-shaped masses attached to the blood-vessels. I have, however, not been able to distinguish them.]

[Tolldt (_l. c._ 1868) described the lymphoid tissue and the blood-vessels of this gland but did not find the corpuscles of Hassall.

Fleischl (_l. c._ 1870) disputed Tolldt’s description; he evidently found the corpuscles of Hassall (see Fig. 211 IV), but he held them to be nerve-cells, and described them as such. He was also of opinion that the blood-vessels open into the intercellular spaces (as in the spleen). This has not been found to be the case by any other observer. Watney (_l. c._ 1882) first described the concentric corpuscles of Hassall as such.

Most writers describe the parenchyma as arranged in lobules. This I have only seen in a part of the gland and under what I believe to be pathological conditions.]

V. THE THYROID GLAND.

*a.* *General description.* A thyroid gland (Fig. 209 _Thy_) is found on either side as a small, triangular, or oval, reddish-coloured body on the dorsal surface of the _M. sternohyoideus_, just before it passes between the _MM. genio-hyoidei_. It lies in the angle formed between the larger and smaller posterior cornua of the hyoid (_HH_, _HH^1_). It is easily found by the presence of a large number of vessels in its neighbourhood, and especially by the large jugular vein, to the ventral surface of which it is intimately attached.

Not uncommonly several smaller supplemental glands are found in the rich anastomosis surrounding the organ.

The dorsal surface of the gland is lobulated, the ventral surface flatter and convex. The glands of opposite sides are seldom symmetrical.

*b.* *Minute structure* (Fig. 212 I and II). [The gland possesses a connective-tissue capsule, which sends in trabeculae to support the vesicles of which the gland is composed.

The vesicles (I and II), which vary greatly in size, are closed cavities, usually of a rounded or oval form, but sometimes branched (Baber). Each vesicle is lined with a single layer of cubical or slightly columnar epithelium (II, _a_), which rests on a delicate basement-membrane of connective-tissue, placed between the epithelium and the surrounding lymphatics (Baber).

Zeiss describes a delicate reticulum between the epithelial cells.

The vesicles always contain mucus (_b_), and are surrounded by a fine anastomosis of blood-vessels (_c_).]

[Illustration: Fig. 212.

Minute structure of the thyroid gland of _Rana esculenta_.--G. H.

I. Section through the gland (Hartnack, Oc. I, Syst. 3).

II. Small portion of above (Hartnack, Oc. I, Syst. 7).

_a_ Epithelium lining the vesicles. _b_ Mucus. _c_ Blood-vessels, injected with blue mass. ]

VI. THE LYMPHATIC GLANDS OF THE HYOID REGION (TONSILS?).

*a.* [*General description.* These are two oval, reddish-coloured, soft lymphatic glands, placed one on each side of the larynx. Frequently they are divided into two or three lobes by more or less deep fissures. They are constant in their occurrence, and are frequently supplemented by one or more smaller glands; each gland has the larynx on its inner side, the _Vena jugularis_ externally, the _M. omohyoideus_ in front, and above the mucous membrane of the pharynx (Tolldt).

*b.* *Minute structure.* The glands consist of dense lymphoid tissue (Fig. 213), but possess in addition one or more large bodies (_a_) which resemble lymphoid follicles in structure. Each is composed of a dense mass of small cells; and the whole follicle is, as in similar follicles of higher animals, sharply differentiated from the rest of the organ.

The glands possess an extremely rich vascular supply, and are frequently pierced by one or more large arterial trunks.

The mucous membrane covering the glands is thinner than that immediately around, but is not perforated.]

[As far as I am aware, Tolldt is the only observer who describes these glands; he makes no mention of the lymphoid follicles.]

[Illustration: Fig. 213.

Part of section through the lymphatic gland (tonsil?) of _Rana esculenta_ (Hartnack, Oc. I, Syst. 13).--G. H.

_a_ Extremely large lymphoid follicle. ]

SECTION VII.

THE URINO-GENITAL SYSTEM, THE ADRENALS, AND THE FAT-BODIES.

THE URINO-GENITAL SYSTEM, ETC.

LITERATURE.

THE URINO-GENITAL ORGANS.

*Adami, J. G.*, On the nature of glomerular activity in the kidney. Journ. of Physiol. 1886. Vol. VI, p. 382.

*Ankermann*, De moturo et evolutione filorum spermaticorum. Regimonti, 1854.

*Ankermann*, Einiges über die Bewegung und Entwicklung der Samenfäden des Frosches. Zeitsch. f. wiss. Zool. 1857. Vol. VIII, p. 129.

*Beale, L. S.*, On very fine nerve-fibres ramifying in certain fibrous tissues, and of trunks and plexuses consisting entirely of fine nerve-fibres in the bladder of the frog. Beale’s Archives of Med. 1864. Vol. IV, pp. 19–251.

*Bergmann, C. G.*, De glandulis suprarenalis. Dissert. Göttingae, 1839.

*Bidder*, Vergleichende Anat. und histol. Untersuchungen über die männlichen Geschlechts- und Harnwerkzeuge der nackten Amphibien. Dorpat, 1846.

*Biondi, D.*, Die Entwicklung der Spermatozoiden. Arch. f. mik. Anat. 1885. Vol. XXV, p. 594.

*Bloomfield, J. E.*, The development of the Spermatozoa. Quart. Journ. Micros. Sci. 1881. New Series. Vol. XXI, p. 415.

*Böttcher, A.*, Ueber den Bau und die Quellungsfähigkeit der Froscheileiter. Virchow’s Arch. 1866. Vol. XXXVII, p. 174.

*Bouillot, J.*, Sur l’épithélium sécréteur du rein des Batrachiens. Compt. rend. 1882. Vol. XCV, No. 14, pp. 603–604.

*Bourne, A. Gibbs*, On certain abnormalities in the common frog, Rana temporaria. Quart. Journ. Micros. Sci. 1884. New Series. Vol. XXIV, pp. 83–86.

*Bowman, W.*, Sur la structure et fonctions des glandules des reins ou corpuscules de Malpighi. Annal. des Sci. Zool. 1843. Series II. Vol. XIX, pp. 108–145.

*Bowman, W.*, On the structure of the Malpighian bodies of the kidney, etc. Phil. Trans. 1842. Pt. I, pp. 57–80.

*Bowman, W.*, Ueber die Structur und den Nutzen der Malpighischen Körper in den Nieren. Froriep’s Notizen, 1842. Vol. XXII, No. 21, coll. 321–324.

*Bowman, W.*, Ueber die Structur und Functionen der Malpighischen Körper in den Nieren. Froriep’s Notizen, 1843. Vol. XXV, No. 12, col. 177.

*Brandt, A.*, Fragmentarische Bemerkungen über das Ovarium des Frosches. Zeitsch. f. wiss. Zool. 1877. Vol. XXVIII, p. 575.

*Budge*, Harnreservoir der Wirbelthiere. Mittheil. aus d. naturw. V. v. Neu-Pommern und Rügen. 1875, p. 103.

*Carus, C. G.*, and *Otto, A. W.*, Erläuterungstafeln zur vergleichenden Anatomie. Leipzig, 1840.

*Crivelli e Maggi*, Alcuni cenni sovra lo studio dei corpi piangiati delle Rane. Rendiconti del Reale Istituto Lombardo de scienze e lettere. 1869. Second Series. Vol. II, p. 716.

*Della Chiaje*, Esistenza della glandule renala ne Batruci et ne Pisci. Napoli, 1837.

*Drasch, O.*, Ueber das Vorkommen zweierlei verschiedener Gefässknäuel in der Niere. Wiener Sitzungsb. 1878. Vol. LXXVI, Part III, p. 79.

*Duncan, J.*, Ueber die Malpighischen Knäuel in der Froschniere. Sitzungsb. d. Acad. zu Wien, 1867. Vol. LVI, Pt. II, p. 6.

*Duval, M.*, and *Wiet*, Ueber die Wanderung der Eier in die Bauchhöhle beim Frosche. Gaz. de Paris, 1880. No. 17, p. 219.

*Duval, M.*, Recherches sur la Spermatogénèse chez la grenouille. Revue Sci. nat. Montpellier, 1880. Vol. II, pp. 121–143.

*Ecker*, Der feinere Bau der Nebennieren, etc. 1846.

*Eimer, T.*, Untersuchungen über den Bau und die Bewegung der Samenfäden. Verhandl. d. phys.-med. Gesell. in Würzburg, 1874. Vol. VI, New Series, p. 93.

*Engelmann*, Zur Physiologie des Ureter. Pflüger’s Arch. f. d. ges. Physiol. 1869. Vol. II p. 243.

*Fürbringer, M.*, Zur vergleichenden Anat. und Entwicklungsgesch. d. Excretionsorgane der Vertebraten. Morph. Jahrb. Vol. IV.

*Fürbringer, M.*, Zur Entwicklung der Amphibienniere. Heidelberg, 1877.

*Gerlach, J.*, Beiträge zur Structurlehre der Niere. Arch. f. Anat. u. Physiol. 1845, p. 378.

*Gibbes, H.*, On the structure of the Spermatozoon. Quart. Journ. Micros. Sci. 1880. Vol. XX, p. 318.

*Goette, A.*, Entwicklungsgeschichte der Unke. Leipzig, 1875.

*Goette, A.*, Kurze Mittheilungen aus der Entwicklungsgeschichte der Unke. Arch. f. mik. Anat. 1873. Vol. IX, p. 396.

*Grunau, H.*, Ueber das Flimmerepithel auf dem Bauchfell des weiblichen Frosches und über den Eileiterbau desselben. Dissert. Königsberg, 1875.

*Grünhagen, A.*, Untersuchungen über Samenentwickelung. Centralbl. f. d. med. Wiss. 1885. Vol. XXIII, p. 481.

*Grünhagen, A.*, Ueber die Spermatogenese bei Rana fusca (temporaria). Centralbl. f. d. med. Wiss. 1885. Vol. XXIII, p. 737.

*Gscheidlen, R.*, Zur Lehre v. d. Nervenendigung in den glatten Muskelfasern. Arch. f. mik. Anat. 1877. Vol. XIV, p. 321.

*Heidenhain, R.*, Mikroskopische Beiträge zur Anatomie und Physiologie der Nieren. Arch. f. mik. Anat. 1874. Vol. X, p. 1.

*Helmann*, Ueber die Entwicklung der Spermatozoen der Wirbelthiere. Dissert. Dorpat, 1879.

*Henle, J.*, Zur Anatomie der Niere. Nachrichten v. d. k. Gesell. d. Wissensch. z. Göttingen, 1862. Vol. X, pp. 4–12; and in Abhandlungen, 1861–62, Vol. X, p. 223.

*Hoffmann, C. K.*, in Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig and Heidelberg, 1873–1879. Vol. VI.

*Hüfner*, Zur vergleichenden Anatomie und Physiologie der Harncanälchen. Diss. Leipzig, 1866.

*Hyrtl*, Ueber die Injection der Wirbelthierniere, etc. Wiener Acad. Sitzungsb. 1863. Vol. XLVII, Pt. I, p. 172.

*Jensen, O. S.*, Recherches sur la spermatogénèse. Archives de Biologie, 1883. Vol. IV.

*Jensen, O. S.*, Ueber die Struktur der Samenkörper bei Säugethieren, Vögeln, und Amphibien. Anat. Anzeiger. 1886.

*Knappe, E.*, Das Biddersche Organ. Morph. Jahrb. 1886. Vol. XI, pp. 489–548.

*Kolessnikow, N.*, Ueber die Eierentwicklung bei Batrachiern und Knochenfischen. Arch. f. mik. Anat. 1878. Vol. XV, p. 382.

*v. Kölliker, A.*, Gewebelehre. Fifth Edition.

*Langer, C.*, Ueber das Lymphgefässsystem des Frosches. Wiener Acad. Sitzungsb. 1867. Vol. LV, Pt. I, p. 621.

*Lavdowsky, M.*, Ueber die Endigung der Nerven in der Harnblase des Frosches. Centralbl. f. d. med. Wiss. 1871, p. 33.

*Lavdowsky, M.*, Die feinere Structur und die Nervenendigungen der Froschharnblase. Arch. f. Anat. u. Physiol. 1872, p. 55.

*Lereboullet, A.*, Recherches sur l’anatomie des organes génitaux des animaux vertébrés. Nov. acta Acad. Leop. Car. 1851. Vol. XXIII, pp. 1–226.

*Leydig, F.*, Anatom.-histol. Untersuchungen über Fische und Reptilien.

*Leydig, F.*, Lehrbuch der Histologie des Menschen und der Thiere. Frankfurt, 1857, p. 508.

*Leydig, F.*, Untersuchungen zur Anatomie und Histologie der Thiere. Bonn, 1883.

*List, J. H.*, Ueber Becherzellen im Blasenepithel des Frosches. Wiener Sitzungsb. 1884, Vol. LXXXIX, Pt. III, pp. 186–210; also in Arch. f. mik. Anat. 1887, Vol. XXIX, p. 147.

*List, J. H.*, Ueber Becherzellen im Blasenepithel des Frosches. Zool. Anzeiger, 1884. No. 169, p. 328.

*List, J. H.*, Ueber einzellige Drüsen im Blasenepithele der Amphibien. Biol. Centralbl. 1885. Vol. V, p. 499.

*Loos, P. A.*, Die Eiweissdrüsen d. Amphibien und Vögel. Zeitsch. f. wiss. Zool. 1881. Vol. XXXV, pp. 478–504.

*Maier, R.*, Die Ganglien in den harnabführenden Wegen des Menschen und einiger Thiere. Virchow’s Arch. 1881. Vol. LXXXV, pp. 49–71.

*Marcussen, J.*, Ueber die Cloake und Harnblase der Frösche. Bull. der phys.-math. Acad. de St. Pétersbourg, 1853. Vol. XI.

*Marshall, A. M.*, On certain abnormal conditions of the reproductive organs in the frog. Journ. of Anat. and Physiol. 1884. Vol. XVIII, p. 121.

*Marshall, A. M.*, The frog. Manchester and London. 2nd Edit. 1885.

*Mecznikow, E.*, Zur vergleichenden Histologie der Niere. Göttinger Nachrichten, 1866, p. 61.

*Meyer, F.*, Beitrag zur Anatomie des Urogenitalsystems der Selachier und Amphibien. Sitzungsb. d. nat. Gesellsch. Leipzig. 1874, p. 38; published 1875.

*Moleschott*, Ein histochemischer und ein histologischer Beitrag zur Kenntniss der Nieren.

*Miescher*, Die Spermatozoen einiger Wirbelthiere. Verhandl. d. naturf. Gesell. in Basel. 1878. Vol. VI.

*Neumann, E.*, Untersuchungen über die Entwickelung der Spermatozoiden. Centralbl. f. d. med. Wiss. 1868. No. 24.

*Neumann, E.*, Untersuchungen über die Entwickelung der Spermatozoiden. Arch. f. mik. Anat. 1875. Vol. XI, p. 292.

*Neumann* and *Grunau*, Drüsen der Froscheileiter. Arch. f. mik. Anat. 1875. Vol. XI, p. 372.

*Nussbaum, N.*, Ueber die Niere der Wirbelthiere. Sitzungsber. Bonn, 1870.

*Nussbaum, N.*, Ueber die Endigung der Wimpertrichter in der Anurenniere. Sitzungsb. d. niederrheinischen Gesell. in Bonn, 1877. Vol. XXXIV, p. 122.

*Nussbaum, N.*, Ueber den Bau und die Thätigkeit der Drüsen. Arch. f. mik. Anat. 1886. Vol. XXVII, p. 442.

*Nussbaum, N.*, Ueber die Secretion der Niere und über die Verbindung der Samen und harnbereitenden Drüsenschläuche in den Nieren der Batrachier. Sitzungsb. d. niederrheinischen naturf. Gesell. in Bonn, 1877. Vol. XXXIV, p. 277.

*Nussbaum, N.*, Fortgesetzte Untersuchungen über die Secretion d. Niere. Pflüger’s Arch. f. d. ges. Physiol. 1878. Vol. XVII, p. 580.

*Nussbaum, N.*, Ueber die Endigung der Wimpertrichter der Niere der Anuren. Zool. Anzeiger, 1880. No. 67, pp. 514–517.

*Nussbaum, N.*, Zur Differenzirung des Geschlechts im Thierreich. Arch. f. mik. Anat. 1880. Vol. XVIII, p. 73.

*Peltier*, Sur les zoospermes de la grenouille. L’Institut. 1838. Vol. VI.

*Perrault, C.*, De generatione ranarum fusca et bona dissertatio, in Actis Eruditorum, 1687.

*Prévost*, Note sur les animalcules spermatiques de la grenouille et de la Salamandre. Mémoires de la société phys. et d’hist. nat. de Genève. Geneva and Paris, 1841–1842. Vol. IX, p. 289.

*Rathke, H.*, Beiträge zur Geschichte der Thierwelt, III Abth.; and Neueste Schr. d. naturf. Gesell. in Danzig. 1825. Vol. I.

*Reger, R.*, Ueber die Malpighischen Knäuel der Nieren und ihre sogenannten Capseln. Arch. f. Anat. u. Physiol. 1864, P. 537.

*Reichert*, On kidney. Jahresbericht über Anatomie in Arch. f. Anat. u. Physiol. 1843, p. 220, etc.

*Remak*, Untersuchungen über die Entwicklung d. Wirbelthiere, p. 128.

*Retzius, G.*, Zur Kenntniss der Spermatozoen. Biol. Untersuchungen. 1881.

*Rideward, W. G.*, On an abnormal genital system in a male of the common frog. Anat. Anz. 1888. Vol. III, p. 333.

*Robinson, C.*, Ueber die Lymphgefasse der abdominal Eingeweide des Frosches. Froriep’s Notizen, 1846. No. 807, col. 225.

*Rösel, A. J.*, Historia naturalis ranarum nostralium. 1758, p. 28.

*Roth*, Untersuchungen über die Drüsensubstanz der Niere. Bern, 1864; and Schweiz. Gesellsch. f. Heilkunde, 1864. Vol. III, pp. 1–34.

*Schiefferdecker*, Ueber einzellige Drüsen in der Blase der Amphibien. Bericht. d. naturf. Ges. in Rostock, 1883.

*Schultze, F. E.*, Das Drüsenepithel der schlauchförmigen Drüsen des Dünn- und Dickdarms und die Becherzellen (Cloaca of frog). Centralbl. f. d. med. Wiss. 1866, p. 161.

*Schultze, M.*, Observationes nonnullae de ovorum ranarum segmentatione. Bonn, 1863.

*Schultze, O.*, Untersuchungen über die Reifung und Befruchtung des Amphibieneies. Zeitsch. f. wiss. Zool. 1887. Vol. XLV, pp. 177–226.

*Schweigger-Seidel, F.*, Ueber die Samenkörperchen und ihre Entwicklung. Arch. f. mik. Anat. 1865. Vol. I, p. 309.

*Solger, B.*, Beiträge zur Kenntniss der Nieren und besonders der Nierenpigmente der niederen Wirbelthiere. Abhandl. d. naturf. Ges. zu Halle, 1882. Vol. XV.

*Spengel, J. W.*, Die Segmentalorgane der Amphibien. Verhandl. d. phys.-med. Gesells. Würzburg. Vol. X, pp. 89–92.

*Spengel, J. W.*, Das Urogenitalsystem der Amphibien. Arbeiten aus d. Zool. Inst. in Würzburg, 1876. Vol. III, pp. 1–114.

*Spengel, J. W.*, Wimpertrichter in der Amphibienniere. Centralbl. f. d. med. Wiss. 1875, p. 369.

*Swammerdam, J.*, Bibblia naturae. Leydae, 1738. Vol. II, p. 796.

*Thompson, A.*, Article ‘Ovum’ in Todd’s Cyclopædia of Anatomy and Physiology, London, 1879. Vol. V, p. 91.

*Tolotschinoff*, Ueber das Verhalten der Nerven zu den glatten Muskelfasern der Froschharnblase. Arch. f. mik. Anat. 1869. Vol. V, p. 509.

*Tornier, O.*, Ueber Bürstenbesätze am Drüsenepithel. Arch. f. mik. Anat. 1886. Vol. XXVII, p. 181.

*v. la Valette St. George*, Spermatologische Beiträge. Arch. f. mik. Anat. 1886, Vol. XXVII, p. 385; and in Stricker’s Gewebelehre, Article ‘Hoden.’

*Valentin*, On kidney. Repertitorium, 1845. Vol. VIII, p. 92.

*Waldeyer, W.*, Eierstock und Ei. Ein Beitrag zur Anatomie und Entwicklungsgesch. der Sexualorgane. Leipzig, 1870.

*Weldon, W. F. R.*, On the suprarenal bodies of vertebrata. Quart. Journ. Micros. Sci. 1885. Vol. XXV, p. 137.

*v. Wittich, W.*, Beiträge zur morphologischen und histologischen Entwicklung der Harn- und Geschlechtswerkzeuge der nackten Amphibien. Zeitsch. f. wiss. Zool. 1853. Vol. IV, p. 152.

*Wolff, W.*, Die Innervation der glatten Muskulatur. Arch. f. mik. Anat. 1882. Vol. XX, p. 361.

THE ADRENALS.

*Bergmann*, De glandulis suprarenalibus. Dissert. Göttingen, 1839.

*Ecker, A.*, Der feinere Bau der Nebennieren beim Menschen und den vier Wirbel-thierklassen. Braunschweig, 1846.

*Frey, H.*, On the suprarenal capsules, in Todd’s Cyclopædia. London, 1849, p. 827.

*Giles, A. E.*, On the development of the fat-bodies in the frog. Quart. Journ. Micros. Sci.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Heidelberg und Leipzig, 1873–1878. Vol. VI, p. 506.

*v. Kölliker, A.*, Handbuch der mikroskopischen Anatomie. Leipzig, 1854. Vol. II, p. 386.

*Leydig*, Lehrbuch der Histologie. Frankfurt a. M. 1857.

*Moers*, Ueber den feineren Bau der Nebennieren. Virchow’s Arch. 1864. Vol. XXIX, p. 336.

*Nagel*, Ueber die Structur der Nebennieren. Arch. f. Anat. u. Physiol. 1830, p. 377.

THE FAT-BODIES.

*Carus*, Lehrbuch der Zootomie. Leipzig, 1818 (describes the fat-bodies as suprarenals).

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Heidelberg und Leipzig, 1873–1878. Vol. VI.

*Marshall, A. Milnes*, The frog. Manchester and London, 1884.

*v. Wittich, W.*, Beiträge zur morphologischen und histologischen Entwicklung der Harn- und Geschlechtswerkzeuge der nackten Amphibien. Zeitsch. f. wiss. Zool. 1853. Vol. IV, p. 152.

THE URINO-GENITAL SYSTEM, THE ADRENALS, ETC.

THE URINO-GENITAL SYSTEM.

By cutting through the meso-rectum the posterior caval vein is seen, as a large vessel, arising by numerous transverse branches from the ventral surfaces of the kidneys and testes (Fig. 214 _Cv_), lying in the median line between the kidneys; by drawing it to one side the dorsal aorta is brought into view (Fig. 214 _Ao_). The testes are placed on the ventral surface of the kidneys, and together with the fat-bodies conceal the anterior portions of these organs. The posterior portions of the kidneys are covered by peritoneum only, and may by seen without further dissection. The kidneys lie dorsal to the peritoneum, and have this membrane on their ventral surfaces only; their dorsal surfaces are in contact with the lumbo-sacral plexus.

The ureters extend from the anterior border of the eighth vertebra to the middle of the urostyle, where they terminate by two orifices in the dorsal wall of the cloaca (Fig. 184).

The testes are entirely surrounded by peritoneum, except a small part (_Hilus_) of the inner surface, where the vessels and ducts enter.

[Illustration: Fig. 214.

The male urino-genital organs.

_Ao_ Aorta. _Cl_ Cloaca. _Cv_ Inferior vena cava. _FK_ Fat-body. _H_ Testis. _N_ Kidney. _S_, _S^1_ Openings of ureters. _Ur_ Ureter. _Vr_ Renal veins. † Appearance of ureters on the ventral surfaces of kidneys. ]

The urino-genital organs are arranged in the same manner in the two sexes; the ovaries corresponding in position with the testes (Fig. 214), that is, they are bilaterally symmetrical, and placed on the ventral surfaces of the kidneys.

The oviducts (Fig. 224 _Ov_) lie externally to the kidneys and ovaries, and course through the whole length of the trunk from the roots of the lungs to the cloaca. The size of the ovaries and oviducts varies very greatly according to the season of the year; at times, the kidneys may be entirely hidden by them.

I. THE URINARY ORGANS.

A. The *kidneys*.

*a.* *General description.* Each kidney (Fig. 215) is a reddish-brown, elongated organ, almost semilunar in shape; the inner border being straight and the outer convex. The organ is flattened from above downwards, and decreases in thickness towards either end. In animals of average size the kidney is about 16 mm. long, and from 6 to 7 mm. broad. The kidneys lie parallel to the vertebrae.

[Illustration: Fig. 215.

The right kidney, seen from the ventral surface.]

The outer border is smooth and even, except at its posterior third, where a slight depression for the ureter exists; the inner border has usually two or three well-marked notches, the hindermost of which is the deepest (Fig. 215). Each notch is continued outwards as a groove, traversing the whole breadth of the ventral surface and containing a branch of the renal portal vein. The ventral surface is, as a whole, slightly concave, grooved, and lobulated; the dorsal surface is smooth and slightly convex.

*b.* [*Minute structure.* The kidney is enclosed in a thin capsule of fibrous tissue (Fig. 220 _Bg_), which sends in fine trabeculae to support the glandular structures and the blood-vessels.]

(1) The *blood-vessels* of the kidney are the renal veins, the renal arteries, and the renal portal vein.

α. The renal portal vein (p. 247) courses along the outer border of the posterior part of the kidney, and then along the outer margin of the dorsal surface; in this course it gives off large branches, which course inwards and forwards and supply numerous lateral twigs. These anastomose to form a network of vessels on the dorsal surface of the organ, from which very numerous large branches course downwards and somewhat inwards to join corresponding branches of the renal veins (Fig. 216 I).

[Illustration: Fig. 216.

The blood-vessels and lymphatics of the kidney.--G. H.

I. Transverse vertical section through kidney. Venous system blue; arteries red (Hartnack, Oc. I, Syst. 3).

II. Part of a horizontal section through kidney. Venous system blue; arteries red (Hartnack, Oc. I, Syst. 3).

III. Part of a transverse vertical section through kidney; lymphatics blue (Hartnack, Oc. I, Syst. 7).

_A_ Ventral surface. _B_ Dorsal surface. _C_ Two arterial twigs uniting before entering the Malpighian body. ]

β. The renal veins (p. 247) form a coarse plexus on the ventral surface of the kidney, from this numerous large branches (Fig. 216 I) course upwards and outwards.

The venous system between the renal portal veins on the dorsal surface, and the renal veins on the ventral surface, are so large that they can scarcely be named capillaries (Hyrtl).

γ. The renal arteries (p. 233) are distributed to the ventral surface of the kidney; their mode of distribution varies in different parts of the organ. A simple arrangement is that shown in Fig. 216 I, where a branch traverses the breadth of the kidney and gives off branches to the Malpighian corpuscles; in one case (_C_) I have seen two twigs passing to the same corpuscle; as a rule, however, each Malpighian corpuscle receives only one twig. A more general arrangement is that the artery courses nearer the ventral surface and in a more winding course, several twigs are then given off close together, from the convex surface of one of the curves, and these course to their respective corpuscles.

In the Malpighian corpuscle the arterial twig forms a series of loops and then passes out to open abruptly into one of the branches of the neighbouring venous anastomosis (Hyrtl).

(2) [The *Malpighian corpuscles* and their *capsules* (Figs. 216 I, 218 III). The corpuscles lie nearer the ventral than the dorsal surface. They are rounded oval bodies, formed of loops of an arterial twig, held together by a small amount of connective-tissue. Each corpuscle is enclosed in a capsule, which it incompletely fills (Fig. 217)[78].

[Footnote 78: See Plate II.

Portions of two transverse vertical sections through the kidney.--G. H.

I. Kidney of _Rana esculenta_, partial injection of the uriniferous tubes with silver nitrate (Hartnack, Oc. I, Syst. 7).

II. Kidney of _Rana temporaria_, stained with borax-carmine (Hartnack, Oc. I, Syst. 7). ]

The capsules are formed of connective-tissue and lined with a flattened epithelium (Fig. 218 III): according to Duncan the fibrous coat is arranged in two layers (III _a_). Towards the opening of the uriniferous tube the epithelium increases in thickness.

According to Hyrtl, the corpuscles are arranged in two layers, a more superficial one and a deeper one; and are of two sizes, the larger being as a rule the more superficial (ventral).]

(3) [The *uriniferous tubes* (Figs. 217 and 218). Each tube originates at a narrow opening on the dorsal surface of a Malpighian capsule. The tube gradually widens and is lined with a short rounded or cubical epithelium (Roth), (Fig. 218 III); each epithelial cell bearing a small number of extremely small cilia (Bowman, Kölliker, Duncan, and others). The cilia of the cells nearest the capsule are directed towards it (Heidenhain), those of the cells further away have an opposite direction (Spengel). This portion of the tube is known as the neck; it courses dorsalwards.

The second portion of the tube (_Tubulus contortus_), (Fig. 218 III, IX, and XII) has a very tortuous course in the dorsal part of the kidney, and then winds towards the ventral surface. This portion is lined with columnar epithelium, which has granular contents, and possesses large distinct nuclei. The cells of this part of the kidney are usually more or less coloured with a golden-yellow pigment. According to Tornier it bears short cilia (Fig. 218 XIV).

[Illustration: Fig. 218.

Various preparations to show the structure of the uriniferous tubes, etc.

I. Three portions of the uriniferous tubes from _Rana esculenta_, from a natural injection with sulphindigotate of sodium (Hartnack, Oc. I, Syst. 3).--G. H.

II. From the third part of a uriniferous tube; short ciliated epithelium, borax-carmine (Hartnack, Oc. I, Syst. 7).--G. H.

III. A Malpighian corpuscle and capsule; shows the capsule of two layers at _a_. After Duncan.

IV. Part of uriniferous tube after natural injection with sulphindigotate of sodium (Hartnack, Oc. I, Syst. 3).--G. H.

V. Transverse section of one of the larger branches of the ureter, from _Rana esculenta_ (Hartnack, Oc. I, Syst. 7).--G. H.

VI. Epithelial lining of the ureter itself while still in the kidney (Hartnack, Oc. I, Syst. 7).--G. H.

VII. Portion of a uriniferous collecting-tube from section in Fig. 217 I, stained with silver (Hartnack, Oc. I, Syst. 7).--G. H.

VIII. Renal epithelium; _a_ to _b_, tubulus contortus; _b_ to _c_, third portion of uriniferous tube; _c_ to _d_, fourth portion of tube. After Heidenhain (enlarged 210 times).

IX. Ciliated cells of the neck, after Duncan.

X. Isolated rod-cells of _Triton taeniatus_, after Heidenhain.

XI. Isolated rod-cells, after Heidenhain (enlarged 300 times).

XII. Isolated cells of the neck, after Heidenhain (enlarged 210 times).

XIII. Portion of the fourth part of a uriniferous tube, after Heidenhain (enlarged 300 times).

XIV. Ciliated epithelium of tubulus contortus, after Tornier (magnified 550 times).

XV. From kidney of _Rana temporaria_, after Spengel.

_a_ Uriniferous tube opening into seminiferous duct. _b_ Dilated seminiferous duct cut longitudinally. _c_ Vas efferens cut transversely. ]

The third portion corresponds with the narrow limb of Henle’s loop; it is lined with ciliated epithelium (Fig. 218 VIII, _b_ to _c_), similar to that in the neck of the tube.

The fourth portion (Fig. 218 VIII, _c_ to _d_, and XIII) represents the wider limb of Henle’s loop. It has a winding course in the ventral part of the kidney, and then ascends dorsally to open into a collecting-tube. The fourth part of the tube is lined with a short, columnar epithelium (Fig. 218 VIII, _c_ to _d_), which has a clear, cuticular, free border, large nucleus, and a peculiar arrangement of the protoplasm, which shows a rod-like structure (Fig. 218 XI).

The collecting-tubes course transversely near the dorsal surface of the kidney (Fig. 217), and the uriniferous tubes meet them at right-angles. They are lined with a short polygonal epithelium (Fig. 218 VII).

The *peritoneal funnels* of the kidney (nephrostomes). Spengel, Meyer, and Hoffmann describe these funnels as existing in the frog; according to them they open on the ventral surface by narrow apertures, and each is connected, by a vertical tubule, with the fourth part of the uriniferous tube (Spengel), but according to Nussbaum, with the neck of the tube. According to Spengel and Meyer the number of these funnels is in Rana from 250 to 360.

According to Wiedersheim the funnels hang free from the ventral surface like so many parasites attached by fine filaments, and do _not_ open on the surface.

Heidenhain (Arch. f. mik. Anat., Vol. X) was unable to find these organs.

Being unable to find any trace of these organs in the kidneys of either R. temporaria or R. esculenta, in microscopic sections or in teased preparations, I inserted canulae into the ureters of both male and female specimens of both species, and injected the uriniferous tubes with a solution of Berlin blue. Although the tubules were, in some cases, completely injected, in no case could I find any trace of a peritoneal funnel, nor was there any escape of the solution from the kidney as would be the case if the funnels were open and communicated with any part of the uriniferous tubes. Even when the pressure was increased to the extent of a column of 25 cm. high of the injection-mass, no escape took place from the surface of the kidney, though in numerous cases the uriniferous tubes were ruptured by the abnormally high pressure.

Properly dissected frogs were placed in 0.6% sodium chloride solution, in which finely divided gamboge was suspended. No trace of ciliary action was, in any case, found on either surface of the kidneys.

One may therefore conclude that if the peritoneal funnels exist in the adult frog (1) they are very difficult to find; (2) they do not form a free communicating path between any part of the uriniferous tubes and the abdominal cavity; (3) their superficial terminations have no free cilia. As before stated I have found no trace of any such organs.

The *lobules* of the kidney. When treated with proper reagents the kidney shows a marked tendency to separate into lobules (Fig. 219 I).

The *lymphatics* of the kidney (Fig. 216 III[79]) form an irregular network of fine canals with elongated meshes. They run chiefly in the direction of the blood-vessels. The large vessels, which supply the kidney, are surrounded by large lymphatics.]

[Footnote 79: See Plate II.

Two portions from a gold preparation of the kidney of _Rana esculenta_.--G. H.

I. Showing the tendency to split into lobules.

II. Nerve-fibres accompanying the blood-vessels.

_a_ Blood-vessels. _b_ Nerves. ]

The *nerves* of the kidney (Fig. 219 II)[79]. Little is known of these. Nerve-fibres have been traced alongside the larger blood-vessel through the greater part of the kidney.

B. The *ureters*.

*a.* *General description.* In the males the ureters are, at the same time, the seminiferous ducts. Each ureter commences on the dorsal surface of the kidney by bifurcating branches, which are continuous with the collecting-tubes of the kidney. In the anterior two-thirds of the kidney the ureter is wholly on the dorsal surface; at the junction of the middle and posterior thirds it winds round to the outer border of the kidney (Fig. 214 _Ur_), and there lies in a groove accompanied by the renal portal vein (Fig. 220 _Ur_ and _Va_), the two organs being intimately attached to the kidney substance and enclosed by the fibrous capsule (_Bg_).

This portion of the ureter possesses a spindle-shaped enlargement, which represents the _Receptaculum seminis_. In _Rana temporaria_ the _Receptaculum seminis_ forms a large saccular dilatation.

In its further course the ureter runs backwards and slightly inwards, converging with its fellow of the opposite side; the ureters lie free in the abdominal cavity, and terminate by two openings placed side by side in a groove on the dorsal wall of the cloaca (Fig. 214 _S_, _S^1_).

In females the ureters are intimately attached to the dilated oviduct, immediately after leaving the kidney; they pursue a similar course to those of the males, but are attached to the oviduct in the whole of their course to the cloaca.

*b. Minute structure.* The ureter is a tube composed of connective-tissue and involuntary muscular fibre, and lined with a mucous membrane. The mucous membrane is thrown into longitudinal folds, and consists, in the larger tubes, of two or three layers of epithelium (Fig. 218 V), that on the free surface is columnar; the deeper cells being rounded or polygonal. The larger branches of the ureter are lined with columnar epithelium (Fig. 218 VI), with small intervening cells. In some parts of the branches the columnar epithelium bears short cilia.

No glands have been found in the ureter or _Receptaculum seminis_; in _Rana temporaria_, however, the _Receptaculum seminis_ possesses large, branching mucous glands (Wiedersheim).

[Illustration: Fig. 220.

Transverse section of the kidney, enlarged.

_Bg_ Connective-tissue capsule. _D_ Dorsal surface. _NC_ Renal parenchyma. _Ur_ Ureter. _V_ Ventral surface. _Va_ Renal portal vein. ]

C. The *bladder*.

*a.* *General description.* The urinary bladder (Fig. 185 _HB_) is closely attached to the ventral wall of the cloaca and is easily distended from that organ. In relation to the animal it is of very large size; in consequence of its being contracted in the middle it has two lobes, which may be of unequal size. The organ is somewhat heart-shaped (Figs. 184 and 185), with the narrow neck attached to the cloaca, into which it opens by a smaller aperture on the ventral surface. The aperture is surrounded by a small fold of mucous membrane.

*b.* [*Minute structure.* The urinary bladder is bounded by a thin, transparent wall, lined internally with mucous membrane, and covered externally by peritoneum.

(1) The muscular coat is formed of a network of fine bands of unstriated muscular fibre (Fig. 221); it is supported and completed by a connective-tissue layer, rich in connective-tissue corpuscles and yellow elastic fibres.

(2) The peritoneal coat is a single layer of endothelial cells derived from the peritoneum and resting on a very thin layer of subperitoneal tissue.

[Illustration: Fig. 221.

Various preparations from the bladder.

I. Silver preparation of the mucous membrane; seen from the surface. After List (enlarged 400 times).

_a_ Cells of the surface. _d_ Goblet-cells. _e_ Young cells.

II. Vertical section of the mucous membrane; after List (enlarged 600 times).

_a_ Cells of upper layer. _b_ Cells of middle layer. _c_ Cells of lower layer.

III. Large multicellular ganglion; after Wolff.

IV. Vertical section from a silver preparation of the mucous membrane; after List (enlarged 600 times).

_a_ Upper layer. _b_ Middle layer. _c_ Lower layer. _d_ Goblet-cells.

V. Small ganglion of bladder; after Wolff.

_a_ Non-medullated nerve-fibre leading to ganglion. _b_ Process of a ganglion cell. ]

(3) The mucous coat is formed of epithelium resting on a layer of loose, areolar tissue. The epithelium (Fig. 221 I, II, and IV) is arranged in three layers: the cells of the uppermost (II and IV, _a_) always present a flat or convex border to the cavity of the organ; seen from their free surfaces (I) they have polygonal outlines intermixed with round apertures belonging to goblet-cells, the remaining surfaces of these cells are serrated. The cells of the middle layer (II and IV, _b_) are polygonal in outline, they are not so tall as the cells of the layer above; all their borders are serrated. The cells of the deepest layer (II and IV, _c_) are more or less pointed above where they project between the cells of the second layer; their lowest surfaces are flattened towards the subepithelial tissue, and all their surfaces are serrated.

The cells of all three layers possess a cell-wall, and finely granular contents, and each cell has a large oval nucleus (List).

The goblet-cells (Fig. 221 I and IV, _d_) vary very much in shape; they are always more or less rounded in outline: they vary greatly in size (from 190 µ to 54 µ in length); some possess ‘feet’ or basal prolongations, in others these are absent. They usually open freely by rounded apertures on the surface of the mucous membrane, but are sometimes closed. The nucleus is placed towards the base of the cell and surrounded by a smaller or larger amount of protoplasm. These cells usually extend into the middle layer of the epithelium, and they probably constitute unicellular mucous glands (List).

(4) The *blood-vessels* of the urinary bladder (p. 235) are very numerous and run in very tortuous courses; they are accompanied by large lymphatics and by nerves.

(5) The *nerves* of the urinary bladder (p. 191) are of both medullated and non-medullated fibres, which course together towards their points of distribution; the non-medullated fibres are, however, much more frequent than the medullated fibres (Wolff).

The non-medullated nerve-fibres stand in close relation with the nerve-ganglia of the bladder. These ganglia may be unicellular, or composed of groups of nerve-cells; the cells vary considerably in shape, round, oval, triangular, and other forms being equally frequent in their occurrence; to some extent the form appears to depend upon the number and position of the processes of the cells. The diameter of the cells varies from 0.05 mm. to 0.1 mm.; the nucleus has a diameter of 0.025 mm., that of the nucleolus measures 0.005 mm. (Wolff).

The cells may be unipolar or multipolar; the former are however rare. The processes of these cells supply the muscle-fibres (Fig. 221 V, _a_), and other non-medullated processes connect the cells with the nerves (V, _b_ (Wolff)).

The number of muscular fibres is far in excess of the number of the fibres of distribution of the ganglia; Wolff hence concludes that the nervous impulse may pass from one muscle-fibre to another.]

II. THE REPRODUCTIVE ORGANS.

A. The *male reproductive organs* are the testes and their ducts.

*a.* *General description.* The relations of the testes have already been given (p. 234); the organs vary much in shape and size in different individuals and with the different seasons; when greatest they are spherical, or of a rounded oval form, occasionally cone-shaped or pear-shaped. The surface of the testes is not smooth, but presents a series of convexities, each corresponding to a lobule of the gland. At the _hilus_ on the inner border the vessels pass to and from the organ, and the _Vasa efferentia_ leave the testis.

[Illustration: Fig. 222.

The male reproductive organs (enlarged).

_CC_ Vasa efferentia within the kidney. _H_ Testis. _LL_ Collecting-tube at inner border of kidney. _N_ Kidney. _Ne_ Vasa efferentia within the mesorchium. _Ur_ Ureter. † Vasa efferentia ending blindly. ]

The number of _Vasa efferentia_ (Fig. 222 I and II) is subject to considerable variation, not only in different animals, but on the two sides of the same animal. In some cases these ducts form a network (I), in other cases this is absent (II); usually the ducts

[Illustration: Fig. 223.

Various preparations from the testis.

I. Various stages of the spermatozoa; from testis of _Rana temporaria_. After Neumann.

II. Section from testis of _Rana esculenta_ (Hartnack, Oc. I, Syst. 7).--G. H.

_a_ Thin connective-tissue capsule. _b_ Trabeculae. _c_ and _d_ Seminiferous tubes.

III. From testis of _Rana temporaria_. After Neumann.

_x_ Rounded epithelium of seminiferous tubes. _y_ Spermatoblasts.

IV. Surface view of seminiferous tube of _Rana temporaria_. After Neumann.

_a_ Granular protoplasmic feet of spermatoblasts. _b_ Rounded epithelium. ]

bifurcate at acute angles, just before entering the kidney. Most of the tubes so formed open into the collecting-tube; a few, however, end blindly in the mesorchium (I, †). The course of the _Vasa efferentia_ from the testis is first inwards, within the mesorchium; on reaching the kidney they curve dorsalwards between that organ and the corresponding testis: the ducts then travel in the ventral surface of the kidney towards its inner border, where they open into a longitudinal canal (Bidder), (Fig. 222 I, _L_). Just before their terminations each duct has an enlargement (I, _C_), the exact import of which is unknown (see also Fig. 218 XV).

The collecting-tubes open into the ureter at the hinder extremity of the kidney.

*b.* [*Minute structure.* The testis possesses a thin connective-tissue capsule underneath its peritoneal covering (Fig. 223 II, _a_); this sends in trabeculae (_b_) towards the centre of the organ, and so encloses the separate lobules. Each seminiferous tube arises from an elongated irregular sinus placed towards the middle of the organ; the tubes (_c_) are slightly convoluted in their course towards the periphery, near which they branch (Spengel). The tubes are from 0.16 mm. to 0.12 mm. in diameter (Kölliker), and are lined with two kinds of cells (Fig. 222 III); the cells (_x_) nearer the periphery are rounded and have large rounded nuclei, the diameters of which vary from 0.013 to 0.02 mm.; these again possess large and distinct nucleoli. The other cells (_y_) are of elongated, spindle-shaped form; and have oval nuclei, with an average length of 0.016 mm. and an average breadth of 0.005 mm. (Neumann).

The rounded cells lie in groups which vary in thickness and arrangement, and are often compressed so as to have polygonal outlines. The spindle cells are arranged so as to radiate from the lumen of the tube to the periphery, at an angle which varies from 45 to 90 degrees; these are the spermatoblasts.

The various changes which the spermatoblasts undergo in the formation of spermatozoa will easily be understood by reference to Fig. 223 I, _a_ to _k_, where _i_ and _k_ represent the fully developed spermatozoa. These have three parts, head, middle part, and tail, the respective lengths of which in the two species are, according to Neumann, the following:--

Head. Middle part. Tail. Rana esculenta 0.0140 mm. 0.0025 mm. 0.040 mm. Rana temporaria 0.0066 " 0.0330 " 0.045 "

At the hilus of the testis the rounded cells of the seminiferous tubes are gradually modified to form short cylindrical cells (0.01 mm. long and 0.006 mm. broad), the spindle cells being absent (Neumann). The _Vasa efferentia_ are also lined with a similar columnar epithelium (Spengel).]

B. The *female reproductive organs*.

The position of these organs has already been given (p. 335).

I. The *ovaries*.

*a.* *General description.*

Each sac-like ovary (Fig. 224) is subdivided by thin-walled septa into numerous complete chambers, to the inner walls of which the ova are attached. The walls of adjacent sacs are intimately attached to each other, and the subdivision corresponds with the external lobulated appearance of the organ. According to Spengel the number of lobules is about fifteen (Rathke nine to thirteen, Brandt nine). Whether this segmentation of the ovary corresponds with the segmentation of the body has not been determined (Spengel). No part corresponding with Bidder’s organ has been found in _Rana esculenta_.

During the breeding season the ovaries undergo an extraordinary increase in size so as to occupy the greater part of the body-cavity and to displace the other viscera. The ovaries are entirely surrounded by peritoneum.

[Illustration: Fig. 224.

The female reproductive organs; the ovary of the right side has been removed.

_N_ Kidney. _O.T._ Opening of the oviduct into pleuro-peritoneal cavity. _Ov_ Oviduct. _Ova_ Ovary. _P_ Opening of oviduct into the cloaca. _S_, _S^1_ Openings of the ureters. _Ut_ Dilated hinder portion of the oviduct. † Groove in which ureters lie. * Fold in groove separating the openings of the ureters. ]

*b.* *Minute structure.* [The layer of peritoneum covering the ovary possesses cilia (Thiry), the ciliated cells being arranged in isolated patches (Schweigger-Seidel, Waldeyer) on the ventral surface of the organ, and on the mesovarium; these patches are sometimes united by very fine connecting lines of ciliated epithelium; the ciliated epithelium is always sharply marked off from that surrounding it (Kolessnikow). Under the peritoneum is a thin layer of connective-tissue, which is prolonged inwards to form the septa above-described. To these septa are attached the ova.

Between the connective-tissue layer and the peritoneum are isolated patches of germinal epithelium (Fig. 225 IV); these are easily distinguished, by the rounded outlines of their cells, from the surrounding epithelial cells (Waldeyer, Kolessnikow). These patches of germinal epithelium measure from 0.093–0.186 mm. in diameter; the germinal cells average 0.0139–0.0232 mm. in diameter (Kolessnikow). The patches are most numerous on the outer surface of the ovary, and particularly so near the mesovarium.

The follicles contained in the ovary have a connective-tissue coat developed in a manner similar to that of higher animals; the primordial ova which they contain have large nuclei (0.0325 mm.). The epithelium of the follicles has an average diameter of 0.0232–0.0325 mm. (Kolessnikow).

Schultze’s description of the ovaries (_l. c._) varies considerably from that of Waldeyer and Kolessnikow. Briefly he describes the ovaries as a series of sacs separated by and lined externally and internally by endothelium; between these two layers are found the germinal epithelium and follicles: the structures being held together by an extremely minute quantity of connective-tissue.]

II. The *oviducts*.

*a.* *General description.* In young animals the oviducts are quite straight, thin-walled, and of small calibre. During the breeding season, however, they undergo an immense increase in size, and become much convoluted; in this state they are forced in between the other abdominal viscera, and usually cover the whole of the kidneys, and sometimes even part of the ovaries (Fig. 224 _Ov_).

The openings of the oviducts into the pleuro-peritoneal cavity (p. 304) are semilunar slits, directed inwards and lined with ciliated epithelium (p. 306).

Immediately behind this opening (_Ostium abdominale_) the oviduct is contracted, and is there narrower than in the rest of its length; beyond this it expands, and then retains an even size nearly to its hinder extremity, where it suddenly expands (Fig. 224 _Ut_). This dilatation gradually diminishes in size as it proceeds backwards towards the cloaca, into which each tube opens on a small papilla. The dilated portions of the tubes lie close together, but do not communicate with each other; the opening of the right tube is always slightly behind that of the left side (Fig. 224 _P_). From the papillae, into which the oviducts open, a fold of mucous membrane extends backwards on the dorsal surface of the cloaca to meet its fellow of the opposite side at an acute angle (Fig. 224 *). The orifices of the ureters are placed within these folds.

[Illustration: Fig. 225.

Preparations from ovary and oviduct.

I. Ciliated epithelium and goblet-cells of the oviduct; after Neumann.

II. Isolated goblet-cells and secretory cells from oviduct; after Neumann.

_a_, _b_, _c_ Goblet-cells. _d_, _e_, _f_ Secretory cells after treatment with Müller’s fluid. _x_ Stoma of secretory cells.

III. Surface view of the ovary; after Kolessnikow.

_a_ Peritoneal endothelium. _b_ Germinal epithelium. ]

*b.* *Minute structure.*

(1) The *tubular portion* of the oviduct has three walls: a peritoneal covering with sub-peritoneal tissue (_a_); a glandular layer (_b_); and an epithelial lining (_c_). Of these the glandular layer forms by far the thickest layer, especially during the breeding season, when it is much increased in thickness. It consists of long cylindrical glands, often bifurcated at their blind, peritoneal ends. The epithelial cells, with which they are lined, have the power of absorbing more than a hundred times their own weight of water (Boettcher). This layer is absent at the anterior opening of the oviduct.

The cells have an average diameter of 0.012 mm., the lumen of the individual glands 0.1 mm. (in spirit-hardened specimens, Neumann). The cells contain small rounded bodies of very varying size, which may exist singly, grouped, or even arranged in rows; they swell on the addition of water. Each cell possesses, in addition, an oval, granular, distinct nucleus. When treated with Müller’s fluid many of the secretory cells have the appearances shown in Fig. 225 II, _d_, _e_, _f_; they each possess an opening (_x_), (Neumann).

According to Neumann the great power of absorbing water, which the oviducts possess, is due to the presence of these bodies, which he names ‘colloid granules.’ The mucous secretion of these glands passes into the oviduct and surrounds the eggs on their passage towards the cloaca: it is due to this secretion that the egg-spawn is so extremely slippery and difficult to handle.

The inner surface of the oviducts is lined with a ciliated, columnar epithelium (Fig. 225 I), containing numerous goblet-cells (I and II).

(2) The *dilated portion* of the oviduct has much thinner walls than the anterior, narrower portion; the glands cease abruptly at the junction of the two parts. The outer coat also contains unstriated muscular fibre; the inner surface is lined with ciliated epithelium similar to that of the anterior portion.

The *lymphatics* of the oviducts form a net with polygonal meshes on their outer surfaces; from this branches pass inwards in the spaces between adjacent glands to the inner surface, where a network with elongated meshes is formed (Langer).

C. [The *Cloaca*.

*a.* *General description.* The cloaca is a short tube lying beneath the urostyle; anteriorly it receives the openings of the ureters, rectum, and bladder; and in the female the openings of the oviducts, in addition: posteriorly it terminates at the anus.

*b.* *Minute structure.* The cloaca is lined internally with a mucous membrane resembling that of the rectum, _e.g._ a simple layer of columnar epithelium, which rests on a submucous, areolar layer.

The outer walls consist of a thick superficial, longitudinal muscular layer, and a deeper, ill-developed, transverse muscular layer.

*c.* *Special muscles of the cloaca.*

(1) The _M. sphincter ani_ surrounds the end of the cloaca from the anus to the tip of the urostyle. It consists of striated muscle.

(2) The _M. compressor cloacae_ arises from the tip of the urostyle, and is inserted into the hinder end of the rectum; it is also attached to the symphysis of the iliac bones; from this point a few fibres pass to the anus (Hoffmann).]

III. THE ADRENALS.

*a.* *General description.* The adrenals are small yellow bodies attached to the renal veins on the ventral surface of the kidney, towards its outer border.

*b.* [*Minute structure.* The superficial layer of the adrenals consists of solid, rounded, or elongated groups of polygonal cells, containing numerous fat-granules; these represent the cortical substance of the corresponding organs of higher animals. The medullary part is present only in small quantity; it consists of small groups of polygonal cells, placed between trabeculae of connective-tissue; both trabeculae and cell-groups are covered with an endothelium. The whole organ is surrounded by a connective-tissue capsule, which sends in trabeculae to support the parenchyma (Hoffmann).

No nerves have been traced into these organs (Eberth).]

[Illustration: Fig. 226.

The male urino-genital organs.

_Ao_ Aorta. _Cl_ Cloaca. _Cv_ Inferior vena cava. _FK_ Fat-body. _N_ Kidney. _S, S1_ Openings of ureters. _T_ Testis. _Ur_ Ureter. _Vr_ Renal veins. † Appearance of ureters on the ventral surfaces of kidneys. ]

IV. THE FAT-BODIES.

*a.* *General description.* The fat-bodies (Fig. 226) are bright yellow, lobulated bodies, placed in front of the testes and ovaries respectively. The greater portion of each organ lies parallel to the long axis of the body, and from its anterior, posterior, and external borders are given off finger-like processes; these may divide dichotomously either near the base or more peripherally. The external processes are much the longest, and in the male often conceal the greater part of the testis (Fig. 226 _FK_). The organs vary greatly in size with the season of the year.

[Illustration: Fig. 227.

Two preparations from the fat-body of _Rana esculenta_[80].--G. H.

[Footnote 80: From specimens collected in November.]

I. Section of fat-body, stained with borax-carmine (Hartnack, Oc. I, Syst. 7).

_b_ Fat-cells. _c_ Adenoid tissue.

II. Three lobes of fat-body of _Rana esculenta_; coarsely injected (Hartnack, Oc. I, Syst. 3).

Arteries striped. Veins shaded. ]

*b.* [*Minute structure.* Each organ is completely surrounded by peritoneum, under which is a very fine layer of connective-tissue. The interior of the organ (Fig. 227 I) consists of large fat-cells with small patches of adenoid tissue interspersed. The organs are extremely vascular; each lobe has a main artery which gives off lateral branches: each of these immediately divides to form two vessels, which run in opposite directions and almost parallel with the main stem; the vessels then break up into a fine network of capillaries.]

SECTION VIII.

THE SKIN AND THE SENSE-ORGANS.

THE SKIN AND THE SENSE-ORGANS.

LITERATURE.

I. THE SKIN.

*Ascherson*, Ueber die Hautdrüsen der Frösche. Arch. f. Anat. u. Physiol. 1810, p. 15.

*Axmann*, Beiträge zur mikroskopischen Anatomie und Physiologie des Ganglien-nervensystems. 1853.

*de Betta*, Erpétologia delle provincie Venete e del Tirolo meridionale. 1857.

*Biesiadecki*, Ueber Basenbildung und Epithelregeneration an der Schwimmhaut des Frosches. Untersuchungen aus d. Krakauer path.-anatom. Institut. 1872, pp. 60–84. Abstract in Centralbl. f. d. med. Wiss. 1873, No. 7, p. 106.

*Bimmermann, E. H.*, Ueber den Einfluss der Nerven auf die Pigmentzellen des Frosches. Dissert. Strasburg, 1878.

*Bimmermann, E. H.*, Ueber den Einfluss der Nerven auf die Pigmentzellen des Frosches. Centralbl. f. d. med. Wiss. 1879, p. 545.

*de Blainville, M. H. M. Ducrotay*, De l’Organisation des animaux. Paris, 1822, pp. 142, 225.

*Bolaw*, Beitrag zur Kenntniss der Amphibienhaut. Göttingen, 1866.

*Bruch*, Beiträge zur Naturgeschichte und Classification der nackten Amphibien. Würzburger naturwiss. Zeitsch. 1864. Vol. III.

*Brücke*, Untersuchungen über den Farbenwechsel des afrikanischen Chamaeleon. Sitzungsb. der Wiener Acad. 1852. Vol. IV, p. 196.

*Bugnion*, Recherches sur les organes sensitifs qui se trouvent dans l’épiderme du Protée et de l’Axolotl. Dissert. Zürich.

*Canini, A.*, Die Endigungen der Nerven in der Haut des Froschlarvenschwanzes. Arch. f. Anat. u. Physiol. 1880, pp. 143–153.

*Ciaccio, J. V.*, Intorno alla minuta fabbrica della pella della Rana esculenta. Palermo, 1866. Giornale di Scienze naturali ed economiche. Vol. II, pp. 103–158.

*Ciaccio, J. V.*, On the distribution of the nerves to the skin of the frog, with physiological remarks on the ganglia connected with the cerebro-spinal nerves. Trans. Micros. Soc. London, 1864. Vol. XII, pp. 15–31.

*Czermak, J. N.*, Ueber die Hautnerven des Frosches. Arch. f. Anat. u. Physiol. 1849, p. 252.

*Da Collin*, Danemarks Froer og Tudser. Naturhist. Tidsskrift. 1870.

*Dewitz*, Ueber das verschiedene Aussehen der gereizten und ruhenden Drüsen im Sehenballe des Laubfrosches. Biol. Centralbl. 1883, p. 558.

*Dogiel*, Neue Untersuchungen über den pupillenerweiterden Muskel, etc. Arch. f. mik. Anat. 1886. Vol. XXVII, p. 403.

*Duméril* et *Bibron*, Erpétologie générale. 1841. Vol. VIII.

*Eberth, C. J.*, Untersuchungen zur normalen und path. Anatomie der Froschhaut. Leipzig, 1869.

*Eberth, C. J.*, Zur Entwickelung der Gewebe im Schwanze der Froschlarven. Arch. f. mik. Anat. 1866. Vol. II, pp. 490–503.

*Eckhard*, Ueber den Bau der Hautdrüsen der Kröten und die Abhängigkeit der Entleerung ihres Secretes vom centralen Nervensystem. Arch. f. Anat. u. Physiol. 1849.

*Ehrmann, S.*, Ueber Nervenendigungen in den Pigmentzellen der Froschhaut. Sitzungsb. der Wiener Acad. 1882. Vol. LXXXIV, Pt. III, pp. 165–170.

*Engelmann, T. W.*, Pflüger’s Arch. f. d. ges. Physiol. 1871, Vol. IV, p. 321, and 1872, Vol. V, pp. 500–513. (Contractile glands in skin of frog.)

*Harless, E.*, Ueber die Chromatophoren des Frosches. Zeitsch. f. wiss. Zool. 1854, Vol. V, p. 372; also in Münchener Gelehrten Anzeiger, 1853, No. 35.

*Harley, G.*, On the organs of cutaneous respiration; principally on those of Rana temporaria. Trans. Micros. Soc. London, 1857. Vol. V, p. 148.

*Hensche, A.*, Ueber die Drüsen und glatten Muskeln in der äusseren Haut von Rana temporaria. Zeitsch. f. wiss. Zool. 1856. Vol. VII, p. 273.

*Henslow*, Way in which toads shed their skin. Annals of Nat. History, 1850, p. 69.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig und Heidelberg, 1873–1878. Vol. VI.

*Huber, O.*, Ueber Brustwarzen bei Rana temporaria, L. Zeitsch. f. wiss. Zool. 1887. Vol. XLV, p. 664.

*Huizinga, D.*, Untersuchungen über die Innervation der Gefäsze in der Schwimmhaut des Frosches. Pflüger’s Arch. 1875. Vol. XI, p. 207.

*Huxley, T. H.*, Tegumentary organs. Todd and Bowman’s Cyclopædia of Anat. and Physiol. p. 500.

*Klein, E.*, On the lymphatic system of the skin and mucous membranes. Quart. Journ. Micros. Sci. 1881. Vol. XXI, pp. 379–406.

*Kölliker, A.*, Stiftchenzellen in der Epidermis von Froschlarven. Zoolog. Anzeiger. 1885.

*Krause*, Handbuch der Gewebelehre. 1862.

*Krukenberg, C. F. W.*, Die Hautfarbstoffe der Amphibien, in Vergleich. Physiol. Studien, by same author, 1882, pp. 43–49.

*Kutschenko, N.*, Ueber die Krappfärbung der Froschgewebe. Arch. f. mik. Anat. 1882. Vol. XXVIII, pp. 360–364.

*Langer*, Ueber das Lymphgefässsystem des Frosches. Wiener Sitzungsberichte. 1867. Vol. LV, pp. 593–636.

*Langerhans*, Anat.-hist. Untersuchungen über Fische und Reptilien. Berlin, 1853. Journal de Medicine. Vol. XI.

*Leboucq, H.*, Recherches sur le développement et la terminaison des nerfs chez les larves des Batraciens. Bull. de l’acad. roy. de Belgique. 1876. Vol. XLI, p. 4.

*Leydig, F.*, Histologisch-anatomische Untersuchungen über Fische und Reptilien. 1853.

*Leydig, F.*, Tastkörperchen und Muskelstruktur. Arch. f. Anat. u. Physiol. 1856, pp. 150–159.

*Leydig, F.*, Lehrbuch der Histologie. 1857.

*Leydig, F.*, Ueber die Nervenendigung in den sogenannten Schleimkanälen der Fische und über entsprechende Organe der durch Kiemen athmenden Amphibien. Arch. f. Anat. u. Physiol. 1861.

*Leydig, F.*, Ueber die Organe eines sechsten Sinnes. Nov. act. acad. Leop. Carol. 1868. Vol. XXXIV, pp. 1–102.

*Leydig, F.*, Ueber die allgemeinen Bedeckungen der Amphibien. Arch. f. mik. Anat. 1876. Vol. XII, p. 119.

*Leydig, F.*, Ueber die Schleichenlurche. Zeitsch. f. wiss. Zool. Vol. XVIII.

*Leydig, F.*, Ueber die Schwanzflosse, Tastkörperchen und Endorgane der Nerven bei Batrachiern. Arch. f. mik. Anat. 1876. Vol. XII, pp. 513–527.

*Leydig, F.*, Die anuren Batrachier der deutschen Fauna. Bonn, 1877, p. 123.

*Lister, J.*, On the cutaneous pigmentary system of the frog. Phil. Trans. 1857. Vol. CXLVIII, p. 627.

*Macallum, A. B.*, The nerve terminations in the cutaneous epithelium of the tadpole. Quart. Journ. Micros. Sci. 1886. Vol. XXVI, p. 53.

*Mayer, A.*, Ueber das Epithelium bei den Amphibien. Froriep’s Notizen, 1839. Vol. IX, coll. 49–51.

*Menke*, Rana rubita, Linn. Zeitschr. Isis von Oken. 1827. Vol. XX, p. 172.

*Merkel*, Ueber die Endigungen der sensiblen Nerven in der Haut der Wirbelthiere. Rostock, 1880.

*Meyer*, Ueber die Abhängigkeit der Gefässe und Pigmentzellen beim Frosch von dem Nerveneinfluss. Virchow’s Arch. 1854. Vol. VI, p. 581.

*Openchowski, T.*, Histologisches zur Innervation der Drüsen. Pflüger’s Arch. 1882. Vol. XXVII, pp. 223–232.

*Pfitzner, W.*, Die Epidermis der Amphibien. Morph. Jahrb. 1880. Vol. VI, p. 469.

*Rainey*, On the structure of the cutaneous follicles of the toad. Quart. Journ. Micros. Sci. Vol. III, p. 257.

*Roesel*, Historia natur. rana. nostrat. Nürnberg, 1758, p. 3, etc.

*Rudneff*, Ueber die epidermiodale Schicht der Froschhaut. Arch. f. mik. Anat. 1865. Vol. I, p. 295.

*Sattler, E. E.*, Die Verwendung des Lapisstiftes zur Untersuchung der Epithelien. Arch. f. mik. Anat. 1882. Vol. XXI, p. 672.

*Schneider*, Historia amphibiorum. 1739.

*Schultze, F. E.*, Epithel und Drüsenzellen. Arch. f. mik. Anat. 1867. Vol. III, p. 145.

*Schultze, F. E.*, Ueber cuticulare Bildungen und Verhornung von Epithelzellen bei den Wirbelthieren. Arch. f. mik. Anat. 1869. Vol. V, p. 295.

*Schultze, M.*, Ueber die Nervenendigung in der Netzhaut des Auges bei Menschen und Thieren. Centralbl. f. med. Wiss. 1869, p. 885.

*Stieda, L.*, Ueber den Bau der Haut des Frosches. Arch. f. Anat. u. Physiol. 1865, pp. 52–66.

*Stricker, S.*, and *Spina, A.*, Untersuchungen über die mechan. Leistungen d. acinösen Drüsen. Wiener med. Jahrb. 1880, p. 355; und Wiener Sitzungsb. 1880. (Skin and Membrana nictitans.)

*Swammerdam, J.*, Biblia naturae. Vol. II, p. 808.

*Szcesny*, Beiträge zur Kenntniss der Textur der Froschhaut. Dissert. inaug. Dorpat, 1867.

*Turner*, Way in which toads shed their skins. Annals of Nat. History, 1850, p. 430.

*Wagner, R.*, Handwörterbuch der Physiologie. Vol. III, p. 389.

*Walter*, Ueber die Drüsen des Daumenballens des Froschmännchens. Verhandl. d. naturf. Vereins der pr. Rheinlande und Westphalen. 1851, p. 351.

*v. Wittich*, Die grüne Farbe der Haut unserer Frösche, etc. Arch. f. Anat. u. Physiol. 1854, p. 41.

*v. Wittich*, Entgegnung auf Herm. Harless’s über die Chromatophoren des Frosches. Arch. f. Anat. u. Physiol. 1854, p. 264.

II. SPECIAL ORGANS OF TACTILE SENSATION.

_a. The lateral sense-organs._

*Beard, J.*, On the segmental sense-organs of the lateral line and on the morphology of the vertebrate auditory organs. Zool. Anz. 1884. Vol. VII, p. 162.

*Bugnion, E.*, Recherches sur les organes sensitifs qui se trouvent dans l’épiderme du Protée et de l’Axolotl. Dissert. inaug. Zürich. Tire du Boll. No. 7, de la société vaucloise des Sc. nat. Vol. XII. Lausanne, 1873. Verhandl. d. schweiz. naturforsch. Gesells. Zürich, 1873. Vol. LVI, p. 49.

*Froriep, A.*, Ueber Anlagen von Sinnesorganen am Facialis, Glossopharyngeus und Vagus. Arch. f. Anat. u. Physiol. 1885.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig and Heidelberg, 1873–1878.

*v. Kölliker, A.*, Ueber neue Sinnesorgane von Froschlarven. Sitzungsb. Würzburg. 1885, p. 79.

*Krause, W.*, Die Nervenendigung innerhalb der terminal Körperchen. Arch. f. mik. Anat. 1880. Vol. XIX, pp. 53–137.

*Leydig, F.*, Ueber die Organe eines sechsten Sinnes. Nova acta Acad. Leopold. Carol. Dresden, 1868. Vol. XXXIV, pp. 1–102.

*Leydig, F.*, Ueber die allgemeinen Bedeckungen der Amphibien. Arch. f. mik. Anat. 1875. Vol. XII, pp. 513–527.

*Leydig, F.*, Ueber Tastkörperchen und Muskelstructur. Arch. f. Anat. u. Physiol. 1856, p. 150.

*Malbranc, M.*, Bemerkung betreffend die Sinnesorgane der Seitenlinie der Amphibien. Centralbl. f. med. Wiss. 1875, p. 5.

*Malbranc, M.*, Von der Seitenlinie und ihren Sinnesorganen bei Amphibien. Zeitsch. f. wiss. Zool. 1876. Vol. XXVI, pp. 24–86.

*Schultze, F. E.*, Ueber die Nervenendigung in den sogenannten Schleimkanälen der Fische und über entsprechende Organe der durch Kiemen athmenden Amphibien. Arch. f. Anat. u. Physiol. 1861, p. 759.

*Schultze, F. E.*, Ueber die Sinnesorgane der Seitenlinie bei Fischen und Amphibien. Arch. f. mik. Anat. 1870. Vol. VI, p. 62.

_b. The touch-corpuscles of Golgi._

*Golgi, C.*, Della terminazione dei nervi nei tendini e di un nuovo apparato nervoso terminale musculo-tendineo. Atti della Società Italiana di scienze naturali. Milan, 1879. Vol. XXI; and abstracted in Centralbl. f. med. Wiss. 1879, p. 725.

*Golgi, C.*, Intorno alla distribuzione e terminazione dei nervi nei tendini dell’ uomo e di altri vertebrali. Estratto dai Rendiconti del R. Istituto Lombardo. Serie II. Vol. XI. Fasc. IX. Milan, 1878. Abstract in Centralbl. f. med. Wiss. 1879. Vol. 41, p. 725.

*Löwe, L.*, Ueber eine eigenthümliche Art von Gelenknervenkörperchen beim Frosch. Arch. f. mik. Anat. 1880. Vol. XVI, p. 613.

III. THE ORGANS OF TASTE.

*Beale, L. S.*, New observations upon the minute anatomy of the frog’s tongue. Phil. Trans. 1865, p. 443.

*Biedermann, W.*, Ueber morphologische Veränderungen der Zungendrüsen des Frosches, etc. Wiener acad. Sitzungsb. 1882. Vol. LXXXVI, Pt. III, p. 67.

*Billroth, T.*, Ueber die Epithelzellen der Froschzunge, etc. Arch. f. Anat. u. Physiol. 1858, p. 159.

*Engelmann, T. W.*, Ueber die Endigungsweise der Geschmacksnerven des Frosches. Centralbl. f. med. Wiss. 1867, p. 785.

*Engelmann, T. W.*, Ueber die Endigungen der Geschmacksnerven in der Zunge des Frosches. Zeitsch. f. wiss. Zool. 1868. Vol. XVIII, p. 142.

*Engelmann, T. W.*, Die Geschmacksorgane. Stricker’s Handbuch der Gewebelehre. 1872.

*Fixsen, C.*, De linguae raninae structura. Dorpat, 1857.

*Gottschau, M.*, Ueber Geschmacksorgane der Wirbelthiere. Biol. Centralbl. 1882, pp. 240–248.

*Hartmann, R.*, Ueber die Endigungsweise der Nerven in den Papillae fungiformes der Froschzunge. Arch. f. Anat. u. Physiol. 1863, p. 634.

*Hoyer*, Mikroskopische Untersuchungen über die Zunge des Frosches. Arch. f. Anat. u. Physiol. 1859, p. 481.

*Hoyer*, Ueber die Epithelzellen der Froschzunge, etc. Arch. f. Anat. u. Physiol. 1858, p. 163; also in Deutscher Klinik, 1857. No. 21.

*Hyrtl*, Ueber abwickelbare Gefässknäuel in der Zunge der Batrachier. Wiener Acad. Sitzungsb. 1863. Vol. XLVIII, Pt. I, p. 437.

*Key, E. A.*, Ueber die Endigungsweise des Geschmacksnerven in der Zunge des Frosches. Arch. f. Anat. u. Physiol. 1861, p. 329.

*Lépine* (On the nerve supply of the glands of the tongue). Arbeiten aus d. physiol. Anstalt zu Leipzig, 1870, p. 113.

*Molin, R.*, Ueber die Theilung der Nervenprimitivröhren in den Papillae fungiformes der Froschzunge. Wiener acad. Sitzungsb. 1849. Vol. III, p. 183.

*Schultze, F. E.*, Die Geschmacksorgane der Froschlarven. Arch. f. mik. Anat. 1870. Vol. VI, p. 407.

*Waller, A.*, Minute structure of the organ of taste in vertebrate animals. Proc. Roy. Soc. 1848. Vol. V, p. 751.

*Waller, A.*, Minute structure of the papillae and nerves of the tongue of the frog and toad. Phil. Trans. 1848. Pt. I, p. 139.

*Waller, A.*, Microscopic examination of some of the principal tissues of the tongue, etc. Phil. Mag. 1847. Vol. XXX, p. 277.

IV. THE NOSE.

*Babuchin*, Das Geruchsorgan, in Stricker’s Handbuch der Gewebelehre. 1872, p. 964.

*de Blainville, M. H. M. Ducrotay*, L’Organisation des animaux. Paris, 1822, p. 328.

*Blaue, J.*, Untersuchungen über den Bau der Nasenschleimhaut bei Fischen und Amphibien, namentlich über Endknorpel als Endapparate des Nervus olfactorius. Arch. f. mik. Anat. 1884. Vol. XXX, pp. 231–309. Zool. Anzeiger. Vol. V, pp. 657–680.

*Born, G.*, Ueber die Nasenhöhlen und den Thränennasengang der Amphibien. Morph. Jahrb. 1875. Vol. II, p. 4.

*Born, G.*, Ueber die Nasenhöhlen und den Thränennasengang der Amphibien. Breslau. Habilit.-Schrift. 1877.

*Born, G.*, Die Nasenhöhlen und der Thränennasengang der amnioten Wirbelthiere. Morph. Jahrb. 1879. Vol. V, p. 62. 1882. Vol. VIII, pp. 188–232.

*v. Brunn*, Die Membrana limitans olfactoria. Centralbl. f. med. Wiss. 1874, p. 709.

*v. Brunn*, Untersuchungen über das Riechepithel. Arch. f. mik. Anat. 1875. Vol. XI, pp. 468–478.

*v. Brunn*, Weitere Untersuchungen über das Riechepithel u. sein Verhalten zum N. olfactorius. Arch. f. mik. Anat. 1880. Vol. XVII, p. 141.

*Cisoff*, Zur Kenntniss der Regio olfactoria. Centralbl. f. med. Wiss. 1874, pp. 689–691.

*Cisoff*, Zur Frage über die Endigung der Riechnerven beim Frosche. Arbeiten der naturf. Gesells. an der Universität Kassan. 1879. Vol. VIII (in Russian).

*Clarke, J. Lockhart*, Ueber den Bau des Bulbus olfactorius und der Geruchsschleimhaut. Zeitsch. f. wiss. Zool. 1862. Vol. XI, p. 31.

*Colossanti*, Untersuchungen über die Durchschneidung des N. olfactorius bei Fröschen. Arch. f. Anat. u. Physiol. 1875.

*Dirkinck-Holmfield-Christmas, J.*, Experimentalle Undersögelen Bijgningen. Nordiskt medicinskt Arkiv., 1883. Vol. XXVI, pp. 50–60.

*Dogiel, A.*, Ueber die Drüsen der Nasenschleimhaut, besonders die Bowmanschen Drüsen. Arch. f. mik. Anat.

*Dogiel, A.*, Ueber den Bau des Geruchsorgans bei Garroirren, Knochenfischen, und Amphibien. Arch. f. mik. Anat. 1887. Vol. XXIX, p. 74.

*Dogiel, A.*, Ueber den Bau des Geruchsorgans bei Fischen und Amphibien. Biol. Centralbl. Vol. I, pp. 428–431.

*Dogiel, A.*, Ueber die Drüsen d. Regio olfactoria. Arch. f. mik. Anat. 1885. Vol. XXVI, p. 50.

*Ecker, E.*, Bericht über die Verhandl. der Gesellschaft für Beförd. der Naturw. zu Freiburg, 1855, p. 199; and in Zeitsch. f. wiss. Zool. 1856, Vol. VIII, p. 303.

*Eckhard, C.*, Beiträge zur Anatomie und Physiologie. Pt. I, 1855, p. 77.

*Eckhard, C.*, Ueber die Endigungsweise der Geruchsnerven. Beiträge zur Anat. u. Physiol. Giessen, 1882. Vol. I, p. 77.

*Erichsen, J.*, De textura nervi olfactorii ejusque ramorum. Dissert. inaug. 1857.

*Exner, S.*, Untersuchungen über die Riechschleimhaut des Frosches. Sitzungsb. der Wiener Acad. 1871. Vol. LXIII, Pt. II, p. 44.

*Exner, S.*, Weitere Studien über die Structur der Riechschleimhaut bei Wirbelthieren. Sitzungsb. der Wiener Acad. 1872. Vol. LXV, Pt. III, p. 7.

*Exner, S.*, Fortgesetzte Studien über die Endigungsweise des Geruchsnerven. Sitzungsb. der Wiener Acad. 1878. Vol. LXXVI, Pt. III, p. 171.

*Gastaldi*, Nuove Ricerche sovra la terminazione del nervo olfatt. Mem. della reale Acad. della scienze di Torino. 1858. Vol. XVII, Series II, p. 369.

*Hoffmann*, Lehrbuch der Anatomie der Sinnesorgane.

*Hoffmann, C. K.*, Ondersockingen over den anat. bouw van de membrana olfactoria en het periph. uitiende van den Nervus olfactorius. Dissert. inaug. 1866.

*Hoffmann, C. K.*, Amphibia in Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig und Heidelberg, 1873–1878. Vol. VI, pp. 335–347.

*Horn, H.*, Ueber die Endschlingen des Geruchsnerven (nervus olfactorius) der Rana temporaria. Arch. f. Anat. u. Physiol. 1850.

*Hoyer, H.*, De tunica mucosa narium textura. Dissert. inaug. Berol., 1857.

*Hoyer, H.*, Ueber die mikroskopischen Verhältnisse der Nasenschleimhaut, etc. Arch. f. Anat. u. Physiol. 1860, p. 50.

*Langer, C.*, Ueber das Lymphgefässsystem des Frosches. Wiener Acad. Sitzungsb. 1867. Vol. LV, Pt. I, p. 615.

*Legal, E.*, Die Nasenhöhlen und der Thränennasengang der amnioten Wirbelthiere. Morph. Jahrb. 1882. Vol. VIII, p. 353.

*Martin*, Studies from the physiological laboratory in the University of Cambridge. Pt. I. 1873.

*Paschutin, V.*, Ueber den Bau der Schleimhaut der Regio olfactorio beim Frosch. Medicinisky Wjestnik. 1872. Nos. 38–40.

*Paschutin, V.*, Ueber den Bau der Schleimhaut der Regio olfactoria des Frosches. Arbeiten aus d. phys. Laborat. Leipzig, 1873.

*Paulsen, E.*, Ueber die Drüsen der Nasenschleimhaut besonders die Bowman’schen Drüsen. Arch. f. mik. Anat. 1886. Vol. XXVI, pp. 307–321.

*Piersol, G. A.*, Beiträge zur Histologie der Harderschen Drüsen der Amphibien. Arch. f. mik. Anat. 1887. Vol. XXIX, p. 594.

*Reichert, B.*, Arch. f. Anat. u. Physiol. 1857, p. 39. Bericht.

*Schultze, M.*, Ueber die Endigungsweise des Geruchsnerven und die Epithelial-gebilde der Nasenschleimhaut. Monatsb. Acad. z. Berlin. 1856, p. 504.

*Schultze, M.*, Untersuchungen über den Bau der Nasenschleimhaut, namentlich die Structur und Endigungsweise der Geruchsnerven bei dem Menschen und den Wirbelthieren. Halle, 1862. Vol. VII, pp. 32–41; also published in Berlin, 1875. Abstract in Centralbl. f. med. Wiss. 1863, p. 97.

*Seeberg*, Disq. microsc. de textura membr. pitnit. nasi. Dorpat, 1855. Dissert. inaug.

*Stirling, W.*, and *Macdonald*, The minute structure of the palatine nerves of the frog and the termination of nerves in blood-vessels and glands. Journ. of Anat. and Physiol. 1884. Vol. XVII, p. 293.

*Wiedersheim, R.*, Ueber die Kopfdrüsen der Amphibien. Sitzungsb. d. phys.-med. Gesell. in Würzburg, 1876. Febr. 5.

*Wiedersheim, R.*, Die Kopfdrüsen der geschwänzten Amphibien und die Glandula intermaxillaris der Anuren. Zeitsch. f. wiss. Zool. 1876. Vol. XXVII, pp. 1–50.

*Wiedersheim, R.*, Lehrbuch der vergl. Anatomie der Wirbelthiere. Pt. I. Jena, 1882.

V. THE EAR.

*Chatin, J.*, Recherches pour servir a l’histoire du noyau dans l’épithelin auditif des batrachiens. Annales des sciences nat. Zool. 1883. Vol. XVI, Series VI, Art. No. 2.

*Comparetti, A.*, in gymnasio patavino observationes anatomicae de aure interna comparatae. Patavii, 1789.

*Crombie, J. M.*, On the membrana tympani. Journ. of Anat. and Physiol. 1883, pp. 523–536.

*Cuvier, G.*, Leçons d’anatomie comparée. Paris, 1800. Vol. II.

*Deiters, O.*, Ueber das innere Gehörorgan der Amphibien. Arch. f. Anat. u. Physiol. 1862, p. 277.

*Eberth, C. J.*, Zur Kenntniss der Verbreitung der glatten Muskelfasern (Tympanic membrane). Zeitsch. f. wiss. Zool. 1863. Vol. XII, p. 364.

*Ferré*, Étude sur la crête auditive chez les vertébrés. Ann. Sci. Nat. Bordeaux. Vol. I, No. III.

*Hasse, C.*, Die Histologie des Bogenapparates und des Steinsacks der Frösche. Zeitsch. f. wiss. Zool. 1868. Vol. XVIII, p. 71.

*Hasse, C.*, Das Gehörorgan der Frösche. Zeitsch. f. wiss. Zool. 1868. Vol. XVIII, p. 359.

*Hasse, C.*, Das knöcherne Labyrinth der Frösche. Anatomische Studien, 2nd Pt. 1872, p. 377.

*Hasse, C.*, Die vergleichende Morphologie und Histologie des häutigen Gehörorgans der Wirbelthiere. Supplement to the Anatomische Studien. Vol. I, 1873.

*Hasse, C.*, Die Lymphbahnen des inneren Ohres der Wirbelthiere. In the Anatomische Studien of Hasse, 1873. No. XIX.

*Hasse, C.*, Das Gehörorgan der Wirbelthiere von Gustav Retzius. Arch. f. Ohrenheilk. 1884. Vol. XXI, pp. 314–324.

*Hoffmann*, Lehrbuch der Anatomie der Sinnesorgane.

*Hoffmann*, Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig and Heidelberg, 1873–1878. Vol. VI, pp. 304–335.

*Ibsen, J.*, Anatomiske Undersögelser over orets Labyrinth. Udgivet vet P. L. Panum. Kjöbenhawn, 1846 (abstract in Virchow and Hirsch’s Jahresb. 1881, p. 88).

*Kuhn*, Ueber das häutige Labyrinth der Amphibien. Arch. f. mik. Anat. 1880. Vol. XVII, pp. 479–550.

*Kuhn*, Zur Anatomie des inneren Ohres der Wirbelthiere. Compt. rend. du III Congrès internat. d’Otologie à Bàle, 1884, pp. 228–238.

*Leydig, F.*, Lehrbuch der Histologie des Menschen und der Thiere. Frankfurt a. M. 1857.

*Leydig, F.*, Ueber neuere den Aquaeductus vestibuli des Menschen und der Thiere betreffende Forschungen. Sitzungsb. d. Niederrheinischen naturf. Gesellsch. in Bonn, 1874. Vol. XXXIV, p. 124.

*Moldenhauer*, Vergleichende Histologie des Trommelfells. Arch. f. Ohrenheilk. 1878, p. 1.

*Pappenheim, S.*, Ueber Verbreitung der Flimmerbewegung. Arch. f. Anat. u. Physiol. 1840, p. 533.

*Retzius, G.*, On hörselnervens ändningssätt i maculae och cristae acusticae. Nordiskt medicinskt arkiv. 1871. Vol. III.

*Retzius, G.*, Zur Kenntniss der Morphologie des inneren Ohres bei Wirbelthieren. Nord. Med. Ark. 1880. Vol. XII, No. 12.

*Retzius, G.*, Zur Kenntniss des Gehörorgans der Wirbelthiere. Arch. f. Anat. u. Physiol. 1880, pp. 235–244.

*Retzius, G.*, Das Gehörorgan der Wirbelthiere. Pts. I and II, 1881. Stockholm.

*Retzius, G.*, Das Gehörorgan der Wirbelthiere. Congr. internat. de Copenhagen. Anatomy, p. 29.

*Retzius, G.*, Das Gehörorgan der Fische und Amphibien. Pt. I, 1881. Stockholm.

*Retzius, G.*, Zur Kenntniss der Morphologie des inneren Ohres bei Wirbelthieren. Nord. Med. Ark. 1880. Vol. XII, p. 6.

*Retzius, G.*, Ueber die peripherische Endigungsweise der Gehörnerven. Biol. Untersuch. Stockholm and Leipzig, pp. 51–61.

*Schultze, F. E.*, Zur Kenntniss der Endigungsweise der Hörnerven bei Fischen und Amphibien. Arch. f. Anat. u. Physiol. 1862, p. 381.

*Stannius, H.*, Handbuch der Zootomie von v. Siebold und Stannius. Berlin, 1856. 2nd Edit., Pt. II.

*Tafani, A.*, L’organo dell’ udito. Firenze, 1885.

*Waldeyer, W.*, Hörnerv und Schnecke. Stricker’s Handbuch der Gewebelehre, pp. 915–963.

*Weber, E.*, Amtlicher Bericht über die neunzehnte Versammlung deutscher Naturforscher und Aerzte in Braunschweig im Sept. 1841. Printed Braunschweig, 1842.

*Windischmann*, De penitiori auris in amphibiis structura Lipsiae, 1831.

VI. THE EYE.

_a. The cornea and sclerotic._

*Angelucci, A.*, Ueber den Bau u. die Entwickelung des vorderen Uvealtractus der Vertebraten. Centralbl. f. d. med. Wiss. 1879. No. 24, p. 417.

*Altmann, R.*, Ueber die Verwerthbarkeit der Corrosion in der mikroskopischen Anatomie. Arch. f. mik. Anat. 1879. Vol. XVI, p. 471 (Corneal corpuscles).

*Arnold, J.*, Die Vorgänge bei der Regeneration epithelialer Gebilde. Virchow’s Arch. 1869. Vol. XLVI, p. 168.

*Arnold, J.*, Experimentale Untersuchungen über die Entwicklung der Blutcapillaren. Virchow’s Arch. 1871. Vol. LIII, p. 70. 1872. Vol. LIV, p. 1.

*Boddaert*, Zur Histologie der Cornea. Centralbl. f. med. Wiss. 1871, p. 337.

*Ciaccio, J. V.*, On the nerves of the cornea and of their distribution in the corneal tissue of man and animals. Trans. Micros. Soc. London, 1863. Vol. XI, p. 77.

*Clasow, E.*, Om corneal epithel. Upsala läkareförenings förhandlingar. 1869. Vol. IV, p. 411.

*Cohnheim, J.*, Ueber die Endigung der sensiblen Nerven in der Hornhaut. Virchow’s Arch. 1867. Vol. XXXVIII, p. 343.

*Durante, F.*, Sulla terminazione dei nervi della cornea. Richerche fatte nel laborat. di anat. normal. Roma, pubbl. dal dott. F. Tocharo. 1873, pp. 81–87.

*Engelmann, T. V.*, Ueber die Hornhaut des Auges. Leipzig, 1867.

*v. Ewetsky*, Ueber das Endothel der Membrana Descemeti. Untersuch. aus d. pathol. Institut. Zürich, 1875. Vol. III.

*Frey, H.*, Handbuch der Histologie und Histochemie.

*Generisch*, Zur Lehre von den Saftkanälchen in der Cornea. Med. Jahrb. der Gesellsch. d. Aerzte in Wien. 1871, p. 1.

*Guye, A. G.*, Over bekercellen en in het byzonder over de bekercellen in de membrana nictitans van den Kïkvonch. Nederl. Tydschrift v. Gewesh. 1868. Vol. II, p. 135.

*Hansen, A.*, Untersuchungen über die entzündlichen Veränderungen der Hornhautkörper. Wiener Med. Jahrb. 1871, p. 210.

*Harpeck, C.*, Ueber die Bedeutung der nach Silberimprägnation auftretenden weissen lücken- und spaltähnlichen Figuren in der Cornea. Arch. f. Anat. u. Physiol. 1864, p. 222.

*Hartmann, R.*, Ueber die durch den Gebrauch der Höllensteinlösung künstlich dargestellten Lymphgefässanhänge, Saftcanälchen und epithelähnlichen Bildungen. Arch. f. Anat. u. Physiol. 1864, p. 235.

*Heiberg, H.*, Ueber die Neubildung des Hornhaut-Epithels. Wiener Med. Jahrb. 1871.

*Heisrath, F.*, Ueber d. Zusammenhang d. vordern Augenkammer mit d. vord. Ciliarvenen. Arch. f. mik. Anat. 1878. Vol. XV, p. 209.

*Helfreich*, Ueber die Nerven der Conjunctiva und Sclera. Würzburg, 1870.

*Henle, J.*, Handbuch der systematischen Anatomie, 1866. Vol. II.

*His, W.*, Untersuchungen über der Bau der Hornhaut, in Verhandlungen der phys.-med. Gesellschaft in Würzburg. 1856. Vol. IV, p. 90.

*His, W.*, Ueber die Einwirkung des salpetersauren Silberoxydes auf die Hornhaut. Schweizerische Zeitsch. f. Heilkunde. 1864. Vol. II, p. 1.

*Hoffmann, F. A.*, Ueber Contractilitätsvorgänge im vorderen Epithel der Froschhornhaut. Diss. Berlin, 1868.

*Hoffmann, F. A.*, Epithelneubildung auf der Cornea. Virchow’s Arch. 1870. Vol. LI, P. 373.

*Hosch, F.*, Ueber die angebliche Contractilität der Knorpelzellen und Hornhaut-körperchen. Pflüger’s Arch. f. d. ges. Physiol. 1873. Vol. VII, p. 515.

*Hoyer, H.*, Ueber den Austritt von Nervenfasern in das Epithel der Hornhaut. Arch. f. Anat. u. Physiol. 1866, pp. 180–195.

*Hoyer, H.*, Ueber die Nerven der Hornhaut. Arch. f. mik. Anat. 1873. Vol. IX, p. 220.

*Klebs, E.*, Das Epithel der hintern Hornhautfläche. Centralbl. f. d. med. Wiss. 1864, p. 513.

*Klein, E.*, Some remarks on the finer nerves of the cornea. Monthly Journ. Micros. Sci. 1872. Vol. VII, pp. 156–164.

*Klein, E.*, Beiträge zur Kenntniss der peripherischen Verzweigung markloser Nervenfasern. Centralbl. f. d. med. Wiss. 1871, p. 594.

*Klemensiewicz, R.*, Karyokinese in den fixen Hornhautzellen bei Entzündung. Centralbl. f. d. med. Wiss. 1884, p. 163.

*v. Kölliker, A.*, Ueber die Nerven der Hornhaut. Mittheilungen der naturforschenden Gesellschaft in Zürich. 1849.

*v. Kölliker, A.*, Ueber die Nervenendigungen in der Hornhaut. Würzb. naturw. Zeitschr. 1866. Vol. VI, p. 121.

*Königstein, L.*, Histologische Notizen. Arch. f. Ophthalmologie. 1881. Vol. XXVII, p. 56.

*Königstein, L.*, Beobachtungen über die Nerven der Cornea und ihre Gefässe. Wiener Sitzungsber. 1877. Vol. LXXVI, Pt. III, p. 17.

*Königstein, L.*, Beobachtungen über die Nerven der Cornea und ihre Gefässe. Wiener Sitzungsber. 1877. Vol. LXXVI, Pt. III, p. 37.

*Krause, W.*, Ueber das vordere Epithel der Cornea. Göttinger Nachrichten, 1870. Arch. f. Anat. u. Physiol. 1870.

*Krause, W.*, Anatomischer Jahresbericht für 1871 in Prager Vierteljahrsschrift.

*Kühne, W.*, Untersuchungen über Protoplasma und die Contractilität. 1864.

*Lavdowsky, M.*, Das Saugadersystem und die Nerven der Cornea. Arch. f. mik. Anat. 1872. Vol. VIII, p. 538.

*Leber, T.*, Zur Kenntniss der Imprägnationsmethoden der Hornhaut und ähnlicher Gewebe. Arch. f. Ophthalmologie. 1867. Vol. XIV, p. 300.

*Leydig, F.*, Lehrbuch der Histologie. 1857.

*Lightbody, W. H.*, Observations on the comparative anatomy of the cornea of vertebrates. Journ. of Anat. and Phys. 1867. Vol. I, p. 15.

*Lipmann, H.*, Ueber die Endigung der Nerven im eigentlichen Gewebe und im hinteren Epithel der Hornhaut des Frosches. Virchow’s Arch. 1869. Vol. XLVIII, p. 218.

*Lott, G.*, Ueber den feineren Bau und die physiologische Regeneration der Epithelien, insbesondere des Cornea-Epithels. Centralbl. f. d. med. Wiss. 1871.

*Moseley, H. N.*, Some remarks on the nerves of the cornea of the rabbit and frog. Quart. Journ. Micros. Sci. 1871. Vol. XI, p. 261.

*Müller, C. F.*, Histologische Untersuchungen über die Cornea. Virchow’s Arch. 1867. Vol. XLI, p. 110.

*v. Recklinghausen, F.*, Notiz über Silberimprägnation. Virchow’s Arch. 1860. Vol. XIX, p. 451.

*v. Recklinghausen, F.*, Die Lymphgefässe und ihre Bedeutung zum Bindegewebe. Berlin, 1862.

*Robinski*, Die Kittsubstanz auf Reaction des Argentum nitricum. Arch. f. Anat. u. Physiol. 1871, p. 184.

*Rollett, A.*, Ueber das Gefüge der Substantia propria corneae. Sitzungsb. Wiener Akad. 1859. Vol. XXXIII, p. 516.

*Rollett, A.*, Ueber die Contractilität der Hornhautkörper und die Hornhauthöhlen. Centralbl. f. d. med. Wiss. 1871, p. 193.

*Rollett, A.*, Ueber die Hornhaut. Stricker’s Gewebelehre. 1872, p. 1091.

*Saemisch, T.*, Beiträge zur normalen und pathologischen Anatomie des Auges (Nerves of Cornea). Leipzig, 1862.

*Sattler, E. E.*, Die Verwendung des Lapisstiftes sur Untersuchung der Epithelien. Arch. f. mik. Anat. 1882. Vol. XXI, p. 672.

*Schalygen, C.*, Ueber Hornhautepithel und besonders über Vermehrung der Zellen desselben. Arch. f. Ophthalmol. 1866. Vol. XII, p. 83.

*Schneider, A.*, Ueber die Vermehrung der Epithelzellen der Hornhaut. Würzb. naturw. Zeitsch. 1862. Vol. III, p. 105.

*Schwalbe, G.*, Ueber ein mit Endothel bekleidetes Höhlensystem zwischen Choroidea und Sclerotica. Central. f. d. med. Wiss. Berlin, 1868. No. 54.

*Schweigger*, Ueber den Bau der Hornhaut. Allg. med. Centralzeitung. Berlin, 1862. No. 4.

*Schweigger-Seidel, F.*, Ueber die Grundsubstanz und die Zellen der Hornhaut des Auges. Berichte d. math.-physik. Classe der Königl. Sächs. Gesellsch. d. Wissenschaft. 1869. Vol. XXI, pp. 305–359.

*Stricker, S.*, Conjunctiva und Sclerotica im Handb. der Lehre von den Geweben des Menschen und der Thiere. 1872, p. 1142.

*Swaen, M. A.*, Des éléments cellulaires et des canaux plastiques dans la cornée de la grenouille. Bulletin de l’Acad. roy. de Belgique. 1876. 2nd Series, Vol. XLII, pp. 144–183.

*Tamamscheff, T.*, Ueber die Membrana Demoursiana. Centralbl. f. d. med. Wiss. Berlin, 1869.

*Waldeyer, W.*, Microscopische Anatomie der Cornea, Sclera, Lider und Conjunctiva, in Handbuch der gesammten Augenheilkunde. 1874.

*Wolff, W.*, Die Nerven der Cornea. Arch. f. mik. Anat. 1882. Vol. XX, p. 373.

*Zielonko, J.*, Ueber die Entwicklung und Proliferation von Epithelien und Endothelien. Arch. f. mik. Anat. 1874. Vol. X, p. 351.

_b. The lens, choroid, iris, appendages, anterior and posterior chambers._

*Altmann, R.*, Ueber Corrosion in der Histologie. Centralbl. f. d. med. Wiss. 1878, p. 245.

*Altmann, R.*, Ueber die Verwerthbarkeit der Corrosion in der mikroskopischen Anatomie. Arch. f. mik. Anat. 1879. Vol. XVI, p. 471 (Blood-vessels of the choroid).

*Angelucci, A.*, Ueber den Bau und die Entwickelung des vorderen Uveatractus der Vertebraten. Centralbl. f. d. med. Wiss. 1879, p. 417.

*Arnold*, Die Linse. Handbuch der gesammten Augenheilkunde. 1874.

*Barkau, A.*, Beiträge zur Entwicklungsgeschichte des Auges der Batrachier. Wiener Sitzungsber. 1866. Vol. LIV, Pt. I, pp. 70–75.

*Becker*, Untersuchungen über den Bau der Linse bei dem Menschen und den Wirbelthieren. Arch. f. Ophthalmologie. 1863. Vol. IX, Pt. II, pp. 1–42.

*Biedermann, W.*, Zur Histologie und Physiologie der Schleimsekretion (Membrana nictitans). Wiener Sitzungsber. 1886. Vol. XCIV.

*Born, G.*, Ueber die Nasenhöhlen und den Thränennasengang der Amphibien. Morph. Jahrb. 1875. Vol. II, p. 4.

*Bubuchin*, Die Linse. In Stricker’s Handb. der Gewebelehre. 1872.

*Burow*, De vasis sanguif. ran. Diss. Regiomonti, 1838.

*Ciaccio, C. V.*, Beobachtungen über den inneren Bau des Glaskörpers im Auge des Menschen und der Wirbelthiere im Allgemeinen. Moleschott’s Untersuchungen. 1870. Vol. X, p. 385.

*Faber, C.*, Der Bau der Iris des Menschen und der Wirbelthiere. Leipzig, 1876.

*Frey*, Handbuch der Histologie und Histochemie des Menschen. 1874.

*Fubini, S.*, Beiträge zum Studium der Krystalllinse. Moleschott’s Untersuchungen. 1876. Vol. XI, p. 291.

*Golubew*, Beiträge zur Kenntniss des Baues und der Entwicklungsgeschichte der Capillargefässe des Frosches. Arch. f. mik. Anat. 1869. Vol. V, p. 49.

*Grünhagen*, Ueber das Vorkommen eines Dilatator pupillae in der Iris. Zeitsch. f. rat. Med. Vol. XXVIII, pp. 178, 186.

*Heisrath, F.*, Ueber den Zusammenhang der vorderen Augenkammer mit den vorderen Ciliarvenen. Arch. f. mik. Anat. 1878. Vol. XV, p. 209.

*Henle, J.*, Zur Anatomie der Crystalllinse. Abhandl. Gesells. d. Wiss. zu Göttingen. 1878. Vol. XXIII.

*Henle, J.*, Zur Entwicklungsgeschichte der Krystalllinse und zur Theilung des Zellkerns. Arch. f. mik. Anat. 1882. Vol. XX, p. 413.

*Hirschberg*, Zur Dioptric und Ophthalmologie der Amphibienaugen. Arch. f. Anat. u. Physiol. 1887, p. 493.

*Iwanoff*, Beiträge zur normalen und pathologischen Anatomie des Froschglaskorpers. Centralbl. f. d. med. Wiss. 1868, p. 129.

*Klein, E.*, On the peripheral distribution of non-medullated nerve-fibres (Nerves of the nictitating membrane). Quart. Journ. Micros. Sci. 1872. Vol. XII, pp. 21–32.

*Koganeï, J.*, Untersuchungen über den Bau der Iris des Menschen und der Wirbelthiere. Arch. f. mik. Anat. 1885. Vol. XXV, p. 1.

*Koganeï, J.*, Untersuchungen über den Bau der Iris. Sitzungsber. d. Acad. d. Wiss. Berlin, 1885, p. 105.

*v. Kölliker, A.*, Handbuch der Gewebelehre. 1867.

*Langer, C.*, Ueber das Lymphgefässsystem des Frosches. Wiener Acad. Sitzungsb. 1867. Vol. LV, Pt. I, p. 603.

*Leydig, F.*, Anatomisch-histologische Untersuchungen über Fische und Reptilien, 1853.

*Leydig, F.*, Lehrbuch der Histologie des Menschen und der Thiere. 1857.

*Manz, W.*, Ueber den Mechanismus der Nickhautbewegung beim Frosche. Berichte über d. Verhandl. d. naturforsch. Gesell. Freiburg, 1862. Vol. II, p. 391.

*Moriggia, A.*, Ueber die beste Darstellungsweise und die Entwicklung der Röhrchen der Krystalllinse. Moleschott’s Untersuchungen. 1870. Vol. X, p. 658.

*Openchowski, T.*, Histologisches zur Innervation der Drüsen. Pflüger’s Arch. f. d. ges. Physiol. 1882. Vol. XXVII, pp. 223–232.

*Petit*, Sur l’œil de la grenouille. Mém. de l’académie d. Sciences, 1737; see also Lehrbuch d. vergleich. Anatomie, Stannius, Berlin, 1846, p. 198.

*Robinski, S.*, Zur Anatomie, Physiologie und Pathologie der Augenlinse des Menschen und der Wirbelthiere. Arch. f. Anat. u. Physiol. 1872, p. 178.

*Robinsky, S.*, Die Augenlinsensterne des Menschen und der Wirbelthiere. Centralbl. f. d. med. Wiss. 1877, p. 51.

*Sattler, E. E.*, Die Verwendung des Lapisstiftes zu Untersuchungen der Epithelien. Arch. f. mik. Anat. 1882. Vol. XXI, p. 672.

*Stricker, S.*, Untersuchungen über die capillaren Blutgefässe in der Nickhaut des Frosches. Wiener Sitzungsb. 1865, Vol. LI, Pt. II, pp. 16–27; and Moleschott’s Untersuchungen, 1866, Vol. X, pp. 168–180.

*Stricker, S.*, Untersuchungen über die mechan. Leistungen d. acirrösen Drüsen. Wiener med. Jahrb. 1880, p. 355; also Wiener Sitzungsb. 1880 (Membrana nictitans and skin); also in Moleschott’s Untersuchungen. 1870. Vol. X, p. 237.

*Stricker, S.*, Studien über den Bau und das Leben der capillaren Blutgefässe. Wiener Sitzungsb. 1866. Vol. LII, Pt. II, p. 379.

*Stricker, S.*, Untersuchungen über die capillaren Blutgefässe in der Nickhaut des Frosches. Moleschott’s Untersuchungen. 1870. Vol. X, p. 168.

*Thin, G.*, Contribution to the anatomy of the lens. Journ. of Anat. and Physiol. 1876. Vol. X, p. 223.

*Valentin*, Handbuch der Physiologie v. Wagner. 1842.

*Virchow, H.*, Ueber die Gefässe im Auge und in der Umgebung des Auges beim Frosche. Zeit. f. wiss. Zool. 1881. Vol. XXXV, pp. 247–281.

*Virchow, H.*, Ueber die Gefässe des Kopfes und des Auges des Frosches. Verhandl. Würzburg. 1881. Vol. XV, p. xxxiv.

*Virchow, H.*, Mittheilungen zur vergleichenden Anatomie des Wirbelthierauges. Versamml. deutsch. Naturf. und Aerzte. Strassburg. 1885, pp. 409, 410.

*Virchow, H.*, Ueber den ciliaren Muskel des Frosches. Verhandl. d. physiol. Gesell. zu Berlin. 1885, p. 571.

*Virchow, H.*, Ueber die verschiedenen Formen des Ligamentum pectinatum iridis. Versamml. d. Naturf. und Aerzte. 1885, p. 409.

*Zimmermann, W.*, Ueber circumvasale Safträume der Glaskörpergefässe von Rana esculenta. Arch. f. mik. Anat. 1886. Vol. XXVII, p. 410.

_c. The retina._

*Babuchin*, Vergleichende histologische Studien. Würzburger naturwissensch. Zeitsch. 1864. Vol. V, p. 127.

*Beauregard, M. H.*, Contribution à l’étude du rouge rétinien. Journ. de l’anat. et de la physiol. 1879. Vol. XV, p. 161.

*Boll, F.*, Zur Anatomie und Physiologie der Retina. Berlin. Acad. Monatsber. 1876, p. 783.

*Dennissenko, G.*, Vorläufige Bemerkungen zur Lehre über den Bau der Netzhaut. Mitt. aus dem embryolog. Institut. d. Wiener Universität, 1880, Vol. II, p. 1; Abstract in Centralbl. f. d. med. Wiss. 1880, P. 739.

*Dennissenko, G.*, Ueber den Bau der äusseren Körnerschicht der Netzhaut bei den Wirbelthieren. Arch. f. mik. Anat. 1881. Vol. XIX, p. 395.

*Dietl, M. J.*, Beitrag zur Kenntniss des feineren Baues der Stäbchenaussenglieder in der Netzhaut des Frosches. Arch. f. Augen- u. Ohrenheilkunde. 1878. Vol. VII, pp. 17–24.

*Dobrowolsky*, Die Doppelzapfen. Arch. f. Anat. u. Physiol. 1871.

*Dobrowolsky*, Zur Anatomie der Retina. Arch. f. Anat. u. Physiol. 1871.

*Ewart, J. C.*, Notes on the minute structure of the retina and vitreous humour. Journ. of Anat. and Physiol. 1875. Vol. IX.

*Ewart, J. C.*, and *Thin, G.*, On the structure of the retina. Journ. of Anat. and Physiol. 1876. Vol. IX, p. 166.

*Frisch*, Gestalten des Choroidalpigments. Wiener Sitzungsber. 1868. Vol. LVIII, pp. 316–320.

*Heinemann, C.*, Beiträge zur Anatomie der Retina. Arch. f. mik. Anat. 1877. Vol. XIV, p. 409.

*Helfreich*, Ophthalmoscopische Mittheilungen über den Purpur der Retina. Centralbl. f. d. med. Wiss. 1877, p. 113.

*Henle* and *Merkel*, Ueber die sogenannte Bindesubstanz der Centralorgane des Nervensystems. Zeitsch. f. rat. Med. 3rd Series, 1869. Vol. XXXIV.

*Hensen*, Ueber das Sehen in der Fovea centralis. Virchow’s Arch. 1867. Vol. XXXIX, p. 75.

*Hoffmann*, Lehrbuch der Anatomie der Sinnesorgane.

*Hoffmann*, Bronn’s Thierbuch. Leipzig and Heidelberg, 1873–1878. Vol. VI, pp. 274–297.

*Hulke, J. W.*, A contribution to the anatomy of the amphibian and reptilian retina. Quart. Journ. Micros. Sci. 1864, Vol. IV, p. 236; and London Ophthalmic Hospital Reports, 1864.

*Hulke, J. W.*, On the retina of amphibia and reptiles. Journ. of Anat. and Physiol. 1867. Vol. I, p. 94.

*Kühne, W.*, Ueber den Sehpurpur. Centralbl. f. d. med. Wiss. 1877, p. 193.

*Kühne, W.*, Fortgesetzte Untersuchungen über die Retina und die Pigmente des Auges. Heidelberger physiol. Untersuch. 1878, Vol. II, p. 89; Abstract in Centralbl. f. d. med. Wiss. 1879, p. 276.

*v. Kölliker, A.*, Zur Anatomie und Physiologie der Retina. Verhandl. d. phys.-med. Gesellsch. Würzburg, 1852. Vol. III, p. 316.

*v. Kölliker, A.*, Microscopische Anatomie. 1854. Vol. II.

*v. Kölliker, A.*, Handbuch der Gewebelehre. 1867.

*Krause, W.*, Die Nervenendigung in der Retina. Arch. f. mik. Anat. 1876. Vol. XII, pp. 742–790.

*Krause, W.*, Die Nervenendigung innerhalb der terminalen Körperchen. Arch. f. mik. Anat. 1881. Vol. XIX, p. 53.

*Landolt*, Beitrag zur Anatomie der Retina vom Frosch, Salamander und Triton. Arch. f. mik. Anat. 1871. Vol. VII, p. 81.

*Leydig, F.*, Anatomisch-histologische Untersuchungen über Fische und Reptilien. 1853.

*Leydig, F.*, Die Farbe der Retina und das Leuchten der Augen. Arch. f. Naturgesch. 1877. Vol. XXXIII, p. 8.

*Manz, W.*, Ueber den Bau der Retina des Frosches. Zeitsch. f. rat. Med. 3rd Series, 1861. Vol. X, pp. 301–322.

*Manz, W.*, Die Ganglienzellen der Froschnetzhaut. Zeitsch. f. rat. Med. 3rd Series, 1866. Vol. XXVIII.

*Merkel*, Zur Kenntniss der Stäbchenschicht der Retina. Arch. f. Anat. u. Physiol. 1870, p. 642.

*Morano, F.*, Die Pigmentschicht der Retina. Arch. f. mik. Anat. 1872. Vol. VIII, p. 81.

*Morano, F.*, Stomata in der Pigmentschicht der Retina. Centralbl. f. d. med. Wiss. 1875, p. 67.

*Müller, H.*, Histologie der Netzhaut. Zeitsch. f. wiss. Zool. 1851–52. Vol. III, p. 234.

*Müller, H.*, Ueber sternförmige Zellen der Retina. Würzb. Verhandl. 1852. Vol. II, pp. 216–218.

*Müller, H.*, Ueber einige Verhältnisse der Netzhaut bei Menschen und Thieren. Würzb. Verhandl. 1853. Vol. IV, p. 96.

*Müller, H.*, and Kölliker, A., Retina-Tafel. Plate XIX in Ecker’s Icones Physiol. Leipzig, 1854.

*Müller, H.*, Observations sur la structure de la rétine de certains animaux. Compt. rend. 1856, Vol. XLIII, p. 743; and Annales hist. nat. 1856, Vol. XVIII, p. 492.

*Müller, H.*, Anatomisch-physiologische Untersuchungen über die Retina des Menschen und der Wirbelthiere. Zeitsch. f. wiss. Zool. 1857. Vol. VIII, p. 27.

*Müller, W.*, Ueber die Stammentwicklung des Sehorgans der Wirbelthiere. Leipzig, 1874, Festgabe an Carl Ludwig; Abstract in Centralbl. f. d. med. Wiss. 1877, pp. 372 and 388.

*Ogneff, J.*, Histogenese der Retina. Centralbl. f. d. med. Wiss. 1881, p. 641.

*Ogneff, J.*, Ueber die moleculäre Schicht und die sogenannte reticuläre Substanz der Retina. Centralbl. f. d. med. Wiss. 1883, p. 801.

*Oppenheimer, L. S.*, Die Stäbchen in der Netzhaut der Froschembryonen. Schenk’s Embryol. Mitt. Wien. 1878, p. 163.

*Ranvier, L.*, Traité technique d’histologie, sixième fasicule. 1882.

*Ritter*, Ueber den Bau der Stäbchen und äusseren Endigungen der Radialfasern an der Netzhaut des Frosches. Arch. f. Ophthalmol. 1859.

*Ritter*, Zur Histologie des Auges. Arch. f. Ophthalmol. 1868. Vol. XI.

*Schifferdecker*, Studien zur vergleichenden Histologie der Retina. Arch. f. mik. Anat. 1886. Vol. XXVIII, p. 305.

*Schultze, M.*, Zur Anatomie und Physiologie der Retina. Arch. f. mik. Anat. 1866. Vol. II, pp. 175–286.

*Schultze, M.*, Ueber Stäbchen und Zapfen der Retina. Arch. f. mik. Anat. 1867. Vol. III, p. 215.

*Schultze, M.*, Bemerkungen zu dem Aufsatze des Dr. W. Steinlin. Arch. f. mik. Anat. 1868. Vol. IV, pp. 10–21.

*Schultze, M.*, Die Retina. Stricker’s Handbuch der Gewebelehre. 1871.

*Schultze, M.*, Ueber die Nervenendigung in der Netzhaut des Auges bei Menschen und bei Thieren. Arch. f. mik. Anat. 1869. Vol. V, p. 380.

*Schwalbe*, Lehrbuch der Anatomie der Sinnesorgane. Erlangen, 1885, p. 392, etc.

*Steinlin, W.*, Zur Anatomie und Physiologie der Retina. Arch. f. mik. Anat. 1868. Vol. IV, p. 10.

THE SKIN AND THE SENSE-ORGANS.

I. THE SKIN AND ITS APPENDAGES.

The general characters and the colouring of the skin have already been described (pp. 4 to 7). The skin consists of the _cutis vera_ or corium, and the cuticle or epidermis, and is possessed of numerous glands.

*a.* The *epidermis* (Figs. 228, 230) consists of several layers of epithelial cells, those of the deepest layer being more or less columnar in form, those of the middle layer shorter and polygonal, while those of the superficial layer are flattened, very transparent, and horny.

All the surfaces of these cells are serrated, the serrations being, however, with difficulty seen on the free surface of the superficial cells (Leydig). Each cell has a distinct nucleus; in the deeper cells the nucleus is oval, broad, and rounded, in the superficial cells flattened and thin.

The surface of the epidermis (Fig. 230) forms a very beautiful mosaic of flat cells, chiefly hexagonal in form, with pale, central, oval nuclei. Here and there two adjacent cells appear to enclose a semilunar space (Fig. 228 _D_); these spaces are occupied by peculiar cells (goblet-cells, E. Schultze; mucous cells, Leydig), which do not belong to the superficial cells but the layer of cells immediately beneath the horny layer (Schultze, Pfitzner). The cells are rounded or flask-shaped, and closely resemble the epithelial goblet-cells or chalice-cells. According to Rudneff they open on the free surface by stomata; this is, however, denied by Schultze and others.

[Illustration: Fig. 228.

Vertical section through the epidermis from the head of _Rana esculenta_; after F. E. Schultze. Magnified 600 times.

_A_ Horny layer. _B_ Middle layer. _C_ Deep layer. _D_ Isolated mucous-cells. ]

[Illustration: Fig. 229.

Vertical section through the skin of the back; after Wiedersheim.

_Co_ Superficial layer of cutis. _Co^1_ Middle layer of cutis. _Co^2_ Deep layer of cutis. _D_ Cutaneous glands. _D^1_ Ducts of cutaneous glands. _Ep_ Epidermis. _H_ Horny layer of epidermis. _P_ Pigment-cells. _W_ Papillae. ]

According to Pfitzner these cells secrete a substance, which has an important function in connection with the process of casting the skin, which consists in the separation of the upper layer from that below brings about a complete shedding of the skin (Wiedersheim).

[Illustration: Fig. 230.

Surface view of epidermis of _Rana temporaria_; after Eberth.

_A_ Epidermal cell. _B_ Stoma-cell. _C_ Attached cuticle from duct of gland. _D_ Protoplasm and nucleus of stoma-cell. ]

[Illustration: Fig. 231.

Nerve terminations in the branched pigment-cells of the cutis; after Ehrmann. Hartnack, Obj. 8, Oc. 3.

I. Pigment ceasing abruptly at junction of nerve.

II. Pigment gradually ceasing along the nerve. ]

[The horny layer is, for the most part, very thin, as it consists of one or two layers of flattened cells only (Schultze), but in some situations, as on the back and especially on the under surface of the toes, it is much thickened, and is then rough.

Deeply pigmented, branched cells, capable of contractile movements, are also found, somewhat sparsely distributed, in the epidermis (Leydig, H. Müller, Schultze).]

*b.* The *cutis* (Fig. 229, _Co_, _Co^1_, _Co^2_). The epidermis is generally attached to the corium by means of a continuous layer of branched cells, which is deeply stained when the animals are fed with madder (Katschenko). Many of these cells are pigmented. This layer is seldom flat, but is raised into papillae and folds, which are repeated by the superimposed epidermis. In addition to this layer the corium has, except in the webs and supplemental toes, three distinct layers of connective-tissue, together with much unstriped muscle-fibre (Eberth).

The *superficial layer* (Fig. 229 _Co_) is a loosely-meshed, much pigmented, vascular layer; it forms a loose support for the numerous glands, and is traversed by numerous nerves.

The *middle layer* (_Co^1_) forms the groundwork of the cutis; it is much firmer and more compact than the superficial layer; in section it appears as a broad band, bounded superficially by a sharp line. It is chiefly composed of closely packed connective-tissue fibres, which have, for the main part, a horizontal or wavy course; at certain points, however, vertical fibres are seen passing towards the surface and hiding the sharp contour (between _Co_ and _Co^1_). At such points the two sets of fibres form a sort of basket-work arrangement.

The *deepest layer* (Fig. 229 _Co^2_) is composed of very delicate, white and yellow elastic fibres, and vessels and nerves; it attaches the whole integument to the underlying organs. By the looseness of its structure it forms an important lymph-space.

[The *muscle-fibre* of the cutis is very unevenly distributed. It is found somewhat freely in the region of the back, the dorsal surface of the head, and the neck; less freely on the dorsal surfaces of the extremities, very sparsely on the abdomen, breast, and ventral surfaces of the extremities; in the feet it appears to be absent (Eberth).

The *pigment* of the skin. As already mentioned pigmented cells occur in the epidermis, but by far the greater quantity of the cutaneous pigment is found in the cutis, and more especially in the loose layer of branched cells, which form the boundary between epidermis and true cutis. These cells, known as chromatophore-cells, have been carefully investigated by Harless. They play an extremely important part in bringing about the well-known changes in the colouring of the skin. Bimmerman has proved that these cells are influenced by stimulation of the nerves supplying the region in which they occur. Ehrmann has been able to trace a direct connection between the nerve-fibres and the pigment-cells (Fig. 231 I, II). In such cases the pigment was sometimes sharply marked off, at others was gradually lost along the nerve.]

*c.* The *papillae* and *ridges* of the skin are classified by Leydig as follows: (1) Small ridges, (2) larger ridges, (3) papillae with touch-bodies, (4) papillae without touch-bodies, (5) papillae with the ducts of glands, (6) capillaries in the form of papillae, (7) small elevations, including the lateral organs.

[All these structures are derived from the cutis, the epithelium above simply repeating the elevation, and being itself either not increased in thickness or only to a slight degree. (For further description of some of these papillae, see Organs of Tactile Sensation, p. 380.)

Peculiar wart-like papillae are found on the articulations of the first phalanges with the metatarsus, on the same articulations and on the articulations between the first and second phalanges of the third and fifth toes, and on the articulations between the first, second, and third phalanges of the fourth toe. These papillae are connected with the long flexor tendons by fine tendinous bands (Klein).

*Temporary papillae* are developed in the females of _Rana temporaria_ during the breeding season; according to O. Huber (_l. c._), who has described them, their distribution and structure is as follows:--

During the breeding season the skin of the sides of the trunk of female specimens of _Rana temporaria_ is rough; the small elevations, to which this roughness is due, are each about the size of the head of a pin, and have the appearance of small, rounded, white or pale rose-coloured, warty growths. The papillae reach their greatest development and are most numerous on the sides of the trunk (Fig. 232 I); they may be traced on to the tympanic membrane, where they are arranged in a ring, and in some cases under the eyes to the sides of the snout.

Anteriorly the papillae are absent from the median portion of the dorsal surface of the trunk, but posteriorly, behind a line joining the anterior extremities of the two iliac bones, the papillae cover the whole surface.

The papillae are large and very numerous around the arms, and pass by gradual, transitionary stages into the ordinary papillae of the region. Further they may be traced backwards along the anterior or extensor surface of the thigh, the upper surface of the leg, foot, and fifth toe. Occasionally a few papillae were found on flexor surfaces of the third and fourth metatarsus, and very rarely were any discovered on the fore-limbs. They occur in no other batrachian of Germany (Huber).

[Illustration: Fig. 232.

I. Diagram to show the distribution of the temporary papillae in _Rana temporaria_; after Huber.

II, III. Vertical sections through a temporary papilla; after Huber. ]

Each papilla (Fig. 232 II and III) consists of a hemispherical elevation of the cutis, and is covered either by a layer of normal epidermis or in some very rare cases the epidermis was slightly thickened. The papilla consists of a firm connective-tissue stroma, and is from 0.2–0.4 mm. in height, 0.4–0.5 mm. broad (after hardening in alcohol). Such glands as exist in the papilla usually open laterally (Fig. 232 III), and the blood-vessels are numerous.

The epidermis covering the papilla is well supplied with nerve-fibres, derived from large ganglion-cells in the papilla (Fig. 232 III). The branched pigment-cells, so numerous in the rest of the skin, are absent from the upper parts of the papillae (Fig. 232 II); the pigment-cells may cease either abruptly or gradually.

The rose-colour of the papillae is due to the presence of a golden red pigment. After the breeding season the papillae are gradually lost, and the pigment-cells wander into the unoccupied parts.

Huber compares the arrangement of the nerves to that of the ‘touch-spots’ of Merkel.

d. The *glands* of the skin are of two kinds, serous and mucous; they have been fully described by Engelmann and Openchowski.

(1) The *serous glands* (Körnerdrüsen, Engelmann) are large, averaging in diameter 0.2–0.4 mm., but others vary in size from 0.13–0.8 mm. in diameter. They are found chiefly on the dorsum of the trunk and arranged in groups, which vary in dimensions from 3–20 mm. in length and 2–4 mm. in breadth. They may be found in any part between the ear-region and the anus, on the dorsal surface of the thigh, especially towards the outer and inner borders. They are found very sparsely distributed on the ventral surface of the trunk and on other parts of the extremities, though as a rule a few are found on the dorsal surface of the feet and near the phalanges. They are wanting in the nictitating membrane.

The glands have a rounded form, with the ducts placed at their superficial poles. The glands possess three coats; externally is a coat of connective-tissue, the fibres of which are arranged closely together, and cross one another at acute angles: these fibres are continuous with the connective-tissue of the surrounding cutis. Inside this coat is a thick layer of muscle-fibre (0.005–0.015 mm.); the muscle-cells are arranged meridionally, with the one pole towards the superficial surface of the gland, the other pole at the deep surface (Hensche). Many of the fibres, however, extend only one-fourth or one-third of this distance.

The innermost coat is a simple layer of epithelial cells, which rests directly on the muscle-layer; no basement-membrane or space of any kind having been discovered between the two layers. When examined in the recent state these cells are conical or cylindrical in shape, and have the appearance of goblet-cells: they possess a delicate but distinct cell-wall, but are open towards the lumen of the gland. One or sometimes two rounded nuclei are found towards the base of the gland, and surrounded by a small amount of granular protoplasm; the rest of the cell is occupied by a mass of small, rounded, highly refractive granules of about 0.002–0.01 mm. in diameter. These granules are also to be found in the protoplasm of the cell; they contain a substance capable of swelling freely, and present many points of resemblance to the granules found in the cells of the oviducts.

These glands represent the poison-glands or lateral glands of toads, and the ear-glands or parotids of Caecilia (Leydig). According to Leroux[81], Gratiolet and Cloëz[82], the reaction of these glands in toads varies; according to du Bois-Reymond[83] the reaction is, in frogs, acid; Engelmann[84] found the reaction of these glands, in frogs, to be neutral, frequently, however, with a tendency to either acidity or alkalinity.

These glands correspond with the ‘large glands’ of Hensche, the ‘contractile glands’ of Stieda, the ‘large, dark glands’ of Eberth, and the ‘large contractile glands’ of Leydig’s earlier publications.

[Footnote 81: Journal de Médicine, Vol. XI, p. 75.]

[Footnote 82: Comptes rendus, 1851, Vol. XXXII, p. 582.]

[Footnote 83: Untersuchungen über thier. Electricität, 1830, Vol. I, p. 17.]

[Footnote 84: Arch. f. d. ges. Physiol., 1852, Vol. V, p. 505.]

(2) The *mucous glands* are, as a rule, smaller, more numerous, and more evenly distributed than the serous glands. Usually they lie in such close proximity as almost to touch one another; according to Engelmann an average number of sixty is found in one square millimeter; on the abdomen 62–68; flexor surfaces of the posterior extremities in some places 76, but in others only 30–40; on the webs only 2–6 to the square millimeter. On the nictitating membrane they are arranged in two or three parallel rows, are large, and closely applied to each other. They are wanting on the deeper surface of the nictitating membrane.

The glands are generally rounded in form and have a short neck (Fig. 229). Glands in the recent condition, and not fully contracted, have a diameter of 0.06–0.21 mm., the majority measure 0.12–0.16 mm. in diameter. The upper pole of the gland is usually placed directly under the boundary between epidermis and cutis, and, as a rule, about 0.06–0.1 mm. beneath the superficial surface of the skin. The duct usually passes directly to the surface, in a straight line.

The structure of the glands corresponds, in general, with that of the serous glands. Externally is a coat of connective-tissue, which is, however, more firmly attached to the muscular coat than in the case of the serous glands, and may easily be mistaken for a structureless basement-membrane[85] (Eberth). The muscular coat is very thin, and consists of 16–20 flat, spindle-shaped fibres; extending from the upper to the lower pole as in the serous glands. At a short distance (0.015–0.022 mm.) from the upper or superficial pole each fibre has an ellipsoid thickening, composed of granular protoplasm, and containing a clear oval nucleus.

[Footnote 85: Openchowski (_l. c._) describes a basement-membrane.]

The inner coat is composed of a single layer of epithelium, placed directly on the muscular coat. The epithelium has a thickness of about 0.01–0.02 mm.; it is, however, usually thicker towards the base than towards the duct. The boundaries between the cells are very indistinct, and so give the epithelium the appearance of a continuous layer of protoplasm. The glandular epithelium is not directly continuous with the epithelium of the duct.

The shape of the cells depends upon their physiological condition. In a state of semi-contraction of the gland, the cells are cubical, and their free borders pushed into the lumen in a slight convexity; when the gland is fully distended the cells are two or three times as broad as deep; in a fully contracted gland the cells are conical or cylindrical. In the first-mentioned condition their diameter varies from 0.006–0.018 mm. The larger glands are estimated to possess about 150 cells, the smaller only thirty to forty (Engelmann).

The cells appear to have no cell-wall, certainly they possess none on their free surfaces. Their protoplasm distends very freely on the addition of water. As a rule some cells are much more granular than others of the same gland; each cell has a rounded oval, clear nucleus, and vacuoles are frequently met with.

The lumen of the gland contains a colourless, transparent, watery fluid, which contains mucous material.

The ducts of the glands are thick-walled cylinders, circular in section. Their diameter varies from 0.02–0.05 mm., their length is equal to the depth of the superimposed epidermis. The wall of the duct is lined with two or three concentric layers of highly refractive, nucleated cells. The cells are arranged parallel to the length of the duct: in transverse section they are sickle-shaped or semilunar. In the upper third or fourth of the duct the inner wall is lined with a cuticle, very resistant to the action of acids or alkalies: it is thrown off with the skin in the process of casting. In the horny layer of the epidermis this cuticle is partially closed by a stoma-cell (Eberth), (Fig. 230), which possesses a tri-radiate opening.

The glands correspond with the ‘non-contractile glands’ of Hensche, the ‘dark and bright glands’ of Stieda, the ‘glandule mezzane, piccole e piccolissime (ad epitelio pavimentoso)’ of Ciaccio, and the ‘small, dark, and medium-sized, bright glands’ of Eberth.

*e.* The *peculiarities* of the *skin* of the *supplemental toe* and *webs*. The supplemental toe presents, in the male, a rounded, oval swelling (Fig. 234 I, _D_), with the end of the digit projecting from the distal end.

Normally this swelling is usually of a grey colour; during the breeding season, however, the swelling enlarges, and becomes of a black or deep brown colour (Leydig).

[Illustration: Fig. 233.

Vertical section through the epidermis of the supplemental toe of _Rana esculenta_; after E. Schultze. Magnified 400 times. ]

The epidermis covering this swelling (Fig. 233) is much thickened and produced into projecting papillae. The cutis also shows a marked thickening and an increase in vascularity; the glands are of the kind described as mucous glands (Engelmann). They present, however, an immense increase in size, and at the same time are so closely applied to one another as to form the main part of the enlargement (see also Organs of Tactile Sensation).

[Illustration: Fig. 234.

I.

Fore-foot of a male frog.

_D_ Glandular swelling on the supplemental toe. _W_ Warty papillae on the inter-phalangeal joints.

II.

Vertical section through the swelling on the supplemental toe of a male frog.

_B_ Blood-vessels. _Co_ Cutis. _D_ Glands. _Ep_ Epidermis. _M_ Muscles. _P_ Pigment-cells. ]

In the *webs* the various layers of the corium are more or less fused together, and cannot be distinguished from each other; the glands are, as a rule, smaller than on the general surface of the skin.

*f.* The *blood-vessels* and *lymphatics* of the skin.

(1) The *blood-vessels* of the skin are arranged in two networks; the one is situated immediately beneath the epidermis, and consists of fine capillaries, forming a fine-meshed network, which enclose the ducts of the glands. The meshes vary considerably in size and shape (Hyrtl and Langer). The second network of vessels is situated under the cutis; the vessels forming it are small, and the meshes formed are large. From this network vertical branches pass to form the superficial network; these branches usually course along the strands of vertical fibres already described, and break up to form capillaries only when they reach the deeper surface of the epidermis (Langer), (Fig. 235 I).

[Illustration: Fig. 235.

The blood-vessels and lymphatics of the skin; after Langer. Arteries striped, lymphatics shaded.

I. Vertical section through skin of thigh. II. Horizontal view of arteries and lymphatics of the skin. III. Peculiar tortuous arteries of the lamina inguinalis. IV. Arteries and lymphatics of the web. ]

In _some situations_, however, the vertical branches divide earlier; this is especially the case in parts where the glands are very closely packed, as in the nictitating membrane, the upper lip, and the swelling of the supplemental toe (in the male). In these parts the division takes place at the deeper surface of the glands (Langer).

A _peculiar arrangement_ of the cutaneous blood-vessels is found in the lamina inguinalis, where a chain of reddish points can be made out with the naked eye; examined more carefully (Fig. 235 III) each reddish point is found to be a complex loop of capillaries. They extend from the skin to the hinder lymph-hearts, where they form a close network which partially invests the lymph-hearts (Langer).

(2) The *lymphatics of the skin* (see also p. 252), like the arteries, reach the deeper surface of the epidermis by coursing along the bands of vertical fibres; they then form a network of capillaries with rounded meshes (Fig. 235 I, II, IV), and lying immediately under the epidermis, and a network which surrounds the various glands. The lymphatic-capillaries are as a rule larger than the blood-capillaries. The lymphatic network lies beneath the blood network, and the vessels of the two systems branch independently (Langer).

In those parts where the glands are placed closely together this arrangement is modified, and corresponds with the modifications found in the blood-capillaries in these regions. The vertical branches divide so as to form a network below the glands, and from this vertical branches pass in the same direction between the glands to form a secondary network on the superficial surface of the glands (Langer).

g. The *nerves* of the skin. The cutis is very richly supplied with both medullated and non-medullated nerves. In the subcutaneous tissue the nerves destined for the skin branch freely to form numerous fine twigs, which, without actually inosculating, form a fine meshwork. From the larger trunks numerous vertical branches pass vertically to form a secondary network, from which both coarse and very fine twigs pass to encircle the glands. The fine fibres which supply the glands are non-medullated and possess oval nuclei; their diameter varies from 0·001–0·002 mm. The number of nerve-fibres is not much smaller than that of the muscle-fibres (Engelmann). (See also Organs of Tactile Sensation.)]

II. THE ORGANS OF TACTILE SENSATION.

The organs of tactile sensation are the nerve-plexus of the epidermis, the touch-spots of Merkel, the lateral sense-organs, and the touch-corpuscles of the tendons.

*a.* [The *nerve-plexus* of the epithelium is very incomplete as compared with the plexus found in the epithelium of the cornea; here and there a few non-medullated fibres have been traced a short distance between the epithelial cells. No such mode of nerve-terminations in the epithelium as is described by Eberth and Macullum in the tadpole can be found in the adult.]

*b.* The *touch-spots*. What knowledge we possess of these organs is due to the labours of Leydig, Ciaccio, Eberth, and more particularly those of Merkel.

At the base of each papilla, which contains such a touch-organ, is found a number of colourless, flattened cells, arranged either in a single layer, or heaped up and connected with very fine nerve-fibres. The flat surface of the cells is parallel to the surface of the body, and they do not form a separate or circumscribed body, they are therefore better spoken of as touch-spots than as true touch-bodies (Merkel). The larger organs are found in the papillae, but smaller ones may be found on any part of the skin.

[Illustration: Fig. 236.

I. Lateral sense-organ of tadpole of frog. Half-schematic.

_c_ Central zone (nerve-epithelium). _Ml_ Membrana limitans. _p_ Peripheral zone (sustentacular cells). _R_ Hyaline tube.

II. Touch-corpuscle from the sheath of a digital tendon of the frog; after Löwe. Schieck, Oc. O., Obj. 9. ]

These organs are best seen in the prominence or swelling upon the supplemental toe during the breeding season; they are numerous on the dorsal surface of the trunk, but occur most frequently on the under surface of the hinder feet (_Planta pedis_). After the breeding season the organs of the thumb undergo a retrogressive change, which results in a network of spindle-shaped and branched cells with fibres (Wiedersheim).

*c.* The *lateral sense-organs* attain their highest development in the tadpole; in the adult the organs have undergone a retrogressive change, the result of which is that the organs are diminished in size; the whole organ sinks by the formation of a tube, which is then closed by a mucous secretion, consequently the organ is functionless: with this loss in function and change in position of the organs a corresponding diminution of the ramus lateralis nervi vagi occurs (Merkel).

Each lateral organ (Fig. 236 I) consists of a slightly elevated papilla, with the centre depressed, and in each may be distinguished a central and a peripheral zone (_c_, _p_). The central zone consists of a group of pear-shaped cells, with the narrower ends directed towards the free surface; each is connected below with a nerve-fibril, while above it bears a short, stiff cilium. The cilia are enclosed in a delicate hyaline tube (_R_), which is open superficially, closed by the papilla below; consequently the cilia are in direct contact with the surrounding medium. The peripheral zone is a layer of pale, flattened, cylindrical cells (_p_); they possess, at their upper borders, a perforated _membrana limitans_ (_Ml_), through which the cilia pass. These cells serve as a support to the central cells, and are themselves surrounded by ordinary epithelial cells.

The distribution and arrangement of the lateral organs is alike in fish and larval amphibia. They are most numerous on the head, where they surround the eye, and are continued forwards to the snout and on to the lower jaw. All these organs on the head are in connection with the trigeminal nerve. A line of these organs passes from the hinder part of the circumference of the eye along the gill-cover to the neck, where the lines of opposite sides are usually, though not constantly, joined by a transverse line of the same organs; thence the lines are continued along the trunk to the tip of the tail. In fish there exists, as a rule, only one pair of such longitudinal lines (_Linea lateralis_); in anura-larvae, proteus, and in all salamanders there are three pairs: of these one pair lies near the vertebral column, the second at the junction of the flank with the abdomen, and the third corresponds to the lateral line in fish (Malbranc).

At an early developmental period each metamere possesses one pair of such lateral organs; in later life, however, this simple arrangement is lost, and each segment usually possesses a group of organs.

The organs of the trunk and tail are supplied by branches of the Ramus lateralis nervi vagi. Both in fish and amphibia a reparative process, by means of fission, occurs; as a consequence the organs are found in various stages of development.

*d.* [The *touch-corpuscles* of Golgi and Löwe (Fig. 236 II) are found on the joints of the digits. They are surrounded by connective-tissue and are spindle-shaped; the two ends of the spindle are glassy in appearance, the middle portion is fibrous. In the thickest part of the corpuscle is a zone of nuclear bodies.

They are regarded as touch-bodies (Golgi and Löwe). Golgi (_l. c._) describes two kinds of touch-organs in connection with muscle and tendon; one class correspond with those just described, he names them ‘nervous muscle-tendon organs.’ The second class he compares with the touch-bodies found in the conjunctiva.]

III. THE ORGANS OF TASTE.

The organs of taste are not confined to the surface of the tongue, but are also found on the mucous membrane of the roof of the mouth, especially in the neighbourhood of the vomerine teeth; on both roof and floor of the mouth these organs can be traced to the commencement of the oesophagus.

[The mucous membrane of the tongue possesses two kinds of papillae and numerous glands.

*a.* The *filiform papillae* are the more numerous; they are conical or thread-like in form, and consist of connective-tissue, with a few striated muscle-fibres; they include blood-capillaries, but no nerves have been traced into them (Leydig). They are covered with ciliated epithelium and goblet-cells.

*b.* The *fungiform papillae* are much larger, and are paler than the filiform papillae. The free ends of these papillae are broader than the bases, and when the epithelium is removed the free ends present a concavity. From the base to the border of the free surface each papilla is covered with the usual oval, ciliated epithelium, but at this border an abrupt transition takes place. The epithelium covering the end of the papillae is of three kinds: goblet-cells, cylindrical cells, and forked cells; the three forms of cells are quite characteristic, and no intermediate transitionary forms are met with.

(1) The *goblet-cells* (Fig. 237 I) are arranged vertically to the free surface of the papilla; they are from 0.020–0.024 mm. in length, and from 0.01–0.02 mm. in diameter. In the lower third of the cell is found a nucleus of about 0.008 mm. in diameter, and this encloses a nucleolus of about 0.001 mm. in diameter. Close underneath the nucleus the cell is contracted to form an irregular process or foot. The contents of the cells are a very finely granular, transparent protoplasm. These cells form the outermost part of the epithelium, covering the end of the papilla; all the cells belonging to the same papilla are of the same size. In consequence of the mutual pressure which they exert on each other they present, in transverse section, six-sided outlines (Fig. 237, 2). The nuclei of adjacent cells are placed at almost exactly the same level. By the action of reagents on these cells very remarkable forms are obtained, in consequence of the protoplasm swelling and being forced upwards (Fig. 237, 5).

[Illustration: Fig. 237.

I. Various parts from the fungiform papillae; after Engelmann.

1. Nerves of a fungiform papilla. Magnified 450 times.

2. Surface view of the epithelium, after five minute’s action of iodized serum. Magnified 600 times.

3. Goblet-cell with adjacent forked cell. Magnified 450 times.

4. Portion of the papilla, after removal of the goblet- and forked cells; only cylindrical cells remaining. Magnified 400 times.

5. Goblet-cell, with swollen contents. Magnified 450 times.

6–13. Various forms of isolated forked cells. Magnified 450 times.

II. Sections of two glands of the tongue; after Biederman.

1. Resting-gland. 2. Gland after stimulation. ]

(2) The *cylindrical cells* (Fig. 237 I) have rounded free extremities, which reach to the general surface of the epithelium; the remainder of the cell is cylindrical except towards its lower extremity, where it is slightly dilated and encloses an oval nucleus: the protoplasm of the cells is very finely granular. These cells rest on the connective-tissue of the papilla, and are in close juxtaposition, so that several hundreds of them are found on one papilla.

The spaces between the upper parts of the cylindrical cells are occupied by the goblet-cells and by the forked cells.

(3) The *third form* of cell found on the fungiform papillae are named *forked cells* (Fig. 237 I) by Engelmann. The body of the cells has an ellipsoidal form, is from 0.006–0.008 mm. in its longer diameter, and 0.003–0.004 mm. in the shorter diameter. Processes arise from both poles. The peripheral processes arise by a short common stem, which then divides into two or rarely three branches; the whole process is from 0.004–0.008 mm. in length, and is always just sufficiently long to reach the general surface of the epithelium: when the peripheral process is long the central is usually shorter, and _vice versâ_.

The central processes arise by a stem from 0.001–0.002 mm. in thickness, which usually divides dichotomously. The length of this process may be as much as 0.025 mm. or almost nil.

The forked cells are about twice as numerous as the goblet-cells, they occupy the spaces between the cylindrical cells and the goblet-cells. The branched central processes form a network on the connective-tissue of the papilla, which is, at this point, perforated by a rich plexus of fine non-medullated nerve-fibrils. It is not decided whether the processes of various cells inosculate. Engelmann regards these forked cells as the taste-cells and as the sensory nerve-endings.

The *bodies* of the fungiform papillae contain blood-vessels and nerves, the latter enter as medullated nerves, but lose the medulla, somewhat abruptly towards the upper end of the papilla, where they form a sort of nerve-cushion (Nervenkissen, Engelmann).]

Taste-organs are also found on the roof and other parts of the mouth, and present many points of resemblance to the lateral sense-organs. Like them they present a peripheral zone and a central zone; the cells of the latter, however, are not longer than the peripheral cells, and possess no cilia (J. van der Hoeven, Merkel).

IV. THE NOSE.

The *anterior nares* or nostrils are two small openings, placed directly in front of the anterior angle of the eye; the distance between the eye and the corresponding nostril being, in the case of adult animals, about five or six millimeters. The anterior nares are surrounded by rims, which are contracted below, and so form very short, tentacular-like prominences.

The *posterior nares* (choanae) are about four millimeters from the anterior nares, consequently the long axis of the nose is, approximately, of this length. (For the external muscles of the nose, see p. 59.)

The *boundaries* of the *nasal cavities* are as follows:--the roof of each cavity is formed by the dorsal plate of the sphenethmoid, the nasal bone, and the premaxillary bone; the floor is formed by the vomer and the palatine bone, the inner wall by the vertical septum of the sphenethmoid, the outer wall by the premaxillary and maxillary bones, the anterior wall by the premaxillary bone, and the posterior wall by the sphenethmoid. The cartilaginous portion of the nasal skeleton (see also p. 27) projects into the general cavity and subdivides it into various sinuses, which have been the subject of careful investigation by Born and Wiedersheim.

*a.* The *nasal cavities* are best examined by means of serial transverse sections; in a section through the anterior nares (Figs. 238, 239) there will be seen three sinuses on either side:--

(1) The *superior sinus* (_on_) is large, rounded, and placed against the cartilaginous septum; the sinus is lined with olfactory epithelium. Posteriorly the sinus extends beyond the posterior nares, and is bounded by the anterior surface of the sphenethmoid. In front it ends in a rounded concavity, likewise lined with olfactory mucous membrane. Opposite the anterior nares the cavity is partially subdivided, by a longitudinal process on the floor, into two cavities; the anterior nares open into the external chambers, and therefore not directly into the main cavity of the superior sinus. The superior sinus communicates with the inferior sinus by a narrow, almost vertical, slit.

(2) The *inferior sinus* (_un_) is narrow and flattened from above downwards; it is placed against the maxillary bone, and represents the maxillary sinus of the frog. Externally it possesses a descending arm.

The inferior sinus is continued backwards and opens on its inner side into the posterior nares, or rather into the mouth. The descending arm extends only a short distance forwards, to terminate near the point where the superior and inferior sinuses communicate by only a narrow opening. This sinus is on the whole broader in front than behind, and has a general direction from without, inwards and forwards underneath the superior sinus.

[Illustration: Fig. 238.]

[Illustration: Fig. 239.

Frontal sections through the nose of two tadpoles; after G. Born.

_A_ Anterior naris. _b_ Cartilaginous floor. _C_ Cutis. _d_ Cartilaginous roof. _Ep_ Epidermis. _gi_ Intermaxillary gland. _gni_ Lower nasal gland. _gns_ Upper nasal gland. _K_ Maxillary sinus. _l_ Concha narium (os lachrymale). _m_ Maxillary bone. _MS_ Oral mucous membrane. _ok_ Cartilage. _on_ Upper blind sac. _R_ Pharyngeal gland. _S_ Nasal septum. _se_ Septum between the upper and lower nasal cavity. _sn_ External blind sac. _T_ Trabeculae. _Th_ Lachrymal duct. _un_ Lower blind sac. ]

(3) The *lateral sinus* (_sn_) is situated in the partition between the superior and inferior sinuses, or rather between the external chamber of the upper sinus and the inferior sinus. The lateral sinus is triangular in form, being narrow in front and broad behind; at its inner posterior angle it opens on the free border of the horizontal partition between the superior and inferior sinuses; this opening is, however, continued along its roof, so that the lateral sinus opens also into the superior sinus.

*b.* The *nasal cartilages*. The two nasal cavities are completely separated by the cartilaginous septum (Figs. 238 and 239 _S_), and are for the most part lined by cartilage. The anterior end is formed of concave cartilages, while the posterior, being situated in the sphenethmoid, is usually more or less ossified in the adult. The posterior wall has two openings: a larger near the septum for the olfactory nerve, and a smaller, more externally, for the nasal branch of the trigeminal nerve.

The anterior wall is more complex than the posterior, being thicker in the middle than at the sides, and possessing three blind sacs for the three sinuses. From the anterior wall two processes project backwards between the sacs and enclose them more or less completely.

Of the three sacs or cavities only the lower is completely surrounded by cartilage. The upper sac is in part bounded by a shell-shaped, concave cartilage (_Concha narium_, of various authors; _Os lachrymale_, Born), which covers it anteriorly and externally, and is attached by a small base to the roof of the lower sac (Fig. 239, _l_), its upper border bounding the anterior naris (Fig. 15). The upper and external parts of the upper sac have no cartilage. The cartilages of the outer wall of the lower, blind sac extend backwards to the point where the maxillary sinus commences to descend: the roof, however, is prolonged further backwards by two small cartilaginous processes; the inner is short, the outer forms the roof of the descending arm of the sinus, and joins a cartilaginous process, which commences at the anterior portion of the roof of the nasal cavity, passes backwards and downwards to a broad plate, and forms an incomplete outer wall to the nasal cavity. There are also three cartilaginous processes--α. One arising from the outer side of the floor at the level of its junction with the anterior wall; it is a flattened process and passes outwards, and bifurcates at its end to meet the premaxillary and maxillary bones (this is the Oberkieferfortsatz of Ecker), (p. 28, Fig. 14 _n″_). β. A delicate process on either side, described by Wiedersheim (see p. 280). γ. The third pair of processes are fully described for the first time by Born; each arises at the lower border of the corresponding _Concha narium_, passes forwards and downwards under the ascending process of the premaxillary to the point where process β is attached to this bone. The processes are flat and approach one another obliquely; in older animals they are united at the point of contact.

At the junction of the anterior wall, the septum, and the floor is a large aperture in the cartilaginous capsule, through which passes the chief nasal branch of the trigeminus, which supplies numerous branches to the intermaxillary gland.

*c.* The *glands* of the *nasal region* are Bowman’s glands, the intermaxillary glands (Wiedersheim), the lower nasal gland (Born), the upper nasal gland (Born), the pharyngeal gland (Born), and the lachrymal duct.

[Illustration: Fig. 240.

I. A. Bowman’s glands in situ from _Rana temporaria_; after C. K. Hoffmann. Magnified 150 times.

B. Section of Bowman’s gland; after C. K. Hoffmann. Magnified 300 times.

II. Vessels of nasal mucous membrane of _Rana esculenta_; after Langer. Blood-vessels striped, lymphatics shaded. ]

(1) The *intermaxillary gland* (see p. 280).

(2) The *lower nasal gland* is placed along the septum and extends as far back as the posterior nares, opening by its ducts (Figs. 238 and 239 _gni_) into the inferior blind sac of the nasal cavity. In histological structure it corresponds with the intermaxillary glands, except that the glandular tubes are somewhat smaller, and the glandular epithelium stains somewhat less easily with carmine (Born).

(3) The *upper nasal gland* occupies the space between the _Concha narium_ (_Os lachrymale_, Born) and the neighbouring cartilages, it also surrounds the anterior naris and the opening of the lachrymal canal (Figs. 238 and 239 _gns_). The numerous ducts open on the mucous membrane covering the oblique cartilage (above described, as passing from in front, downwards and backwards, and forming an incomplete outer wall of the cavity), and its hinder prolongation.

(4) The *pharyngeal gland* is placed transversely behind the posterior nares, and surrounds the vomerine teeth. A portion of the ducts open into the posterior nares, the remainder on the mucous membrane of the pharyngo-oral cavity at two symmetrically placed points (Fig. 238 _R_).

(5) The *lachrymal duct* (see p. 428) opens into the nasal cavity at the point where the lateral sinus opens into the external chamber of the superior nasal sinus.

(6) [The *glands* of *Bowman* (Fig. 240 I) are freely distributed in the nasal mucous membrane. Each gland is usually rounded or flask-shaped, and consists of a single layer of large epithelial cells possessing distinct nuclei and nucleoli. The epithelium of the glands possesses no basement membrane (M. Schultze and Hoffmann[86]), but is bounded externally by a layer of nerve-fibres and connective-tissue.

[Footnote 86: Paschutin describes a basement membrane.]

The glands situated more superficially have straight ducts opening on the surface; those placed more deeply have usually curved ducts (Paschutin).]

*d.* The *mucous membrane* of the nasal cavities. That part of the superior sinus immediately around the anterior naris is lined with stratified epithelium; the rest of the nasal cavity is lined with columnar ciliated epithelium The epithelial layer rests on a subepithelial network, and this again on a submucous connective-tissue layer possessing numerous vessels and nerves.

(1) The *epithelial layer* (Fig. 241) consists of columnar cells, which in the olfactory region are of two kinds; in other regions the epithelium consists of closely-applied ciliated, thick cells, possessing large oval nuclei, and having irregular, branched bases or ‘feet.’ The cells are 0.032–0.048 mm. long; the nuclei 0.016–0.018 mm long, and 0.006–0.008 mm. broad. The free borders of the cells bear a number of fine cilia.

In the olfactory region a second set of cells, olfactory cells, are met with; these cells (Fig. 241 II) possess each an oval body, enclosing a large nucleus, and a peripheral and central process. The peripheral processes reach to the general surface of the surrounding epithelium and there terminate in a number (5–8) of stiff cilia; these cilia are sometimes 0.09 mm. long, they are thicker at their bases than the ordinary cilia (Schultze); according to Hoffmann, a second system of stiffer and longer cilia is met with; of which each olfactory cell possesses as a rule only one. The bodies of the olfactory cells are 0.009–0.010 mm. long, and 0.007–0.008 mm. broad; the peripheral processes vary considerably in length, according to the position of the body (0.03–0.05 mm.). The central processes vary from 0.02–0.03 mm. in length. The peripheral processes are considerably thicker than the central processes. No _membrana limitans olfactoria_ has been discovered in the frog.

(2) The *second layer* consists of a network of processes belonging to the bases of the central processes of the superimposed epithelial and olfactory cells. Numerous highly refractive nuclei possessing nucleoli are situated in the meshes of this network; they correspond in all particulars with the nuclei of the olfactory cells (M. Schultze). According to Exner the branched processes of the epithelial cells and of the olfactory cells unite to form a complex plexus. Other observers, Paschutin, Cissoff, v. Brunn, Schultze, and Hoffmann oppose this view, and hold that the central processes of the olfactory cells do not unite with the processes of the epithelial cells, but that they are in direct continuity with the fibrils of the olfactory nerve. This view is probably correct.

[Illustration: Fig. 241.

Separations from the olfactory mucous membrane of _Rana temporaria_; after C. K. Hoffmann.

I. Surface view of the olfactory mucous membrane. Magnified 350 times.

II. Epithelial and olfactory cells. Magnified 600 times.

III. Epithelial cells. Magnified 600 times. ]

The submucous layer has a loose connective-tissue matrix, which encloses the glands, nerves, and vessels; according to Paschutin two pigment-layers may be distinguished: the one, immediately under the middle layer of this mucous membrane, is continuous and deeply pigmented; the second is deeper and does not form a continuous layer. This layer is extremely rich in blood-vessels and lymphatics (Langer and Paschutin), (Fig. 240 II). The lymphatics are relatively very large and are very numerous (Langer).

In this layer the central processes of the olfactory cells form bundles of fibres, lying parallel with the surface of the mucous membrane (Paschutin, Cissoff, and Schultze).]

V. THE EAR.

(Re-written by the translator from Das Gehörorgan der Wirbelthiere, by G. Retzius, 1881.)

The organ of hearing is divisible into two parts, the tympanum or middle ear, and the labyrinth or internal ear; an external ear is absent, unless a very slight depression of the tympanic membrane be regarded as such.

A. The *tympanum* (_Cavum tympani_) is a cavity, bounded externally by the tympanic membrane and internally by the capsule of the internal ear; it communicates by means of the Eustachian tube (tuba Eustachii) with the pharyngo-oral cavity (Fig. 178).

*a.* The *tympanic membrane* lies immediately underneath the skin, but can be separated from that structure; externally it possesses a very slight depression, the only trace of an external ear found in the frog.

The tympanic membrane is of a rounded oval form, being a little wider in the transverse than in the longitudinal diameter; the membrane is directed outwards.

After detaching the skin (Fig. 242 I) the membrane is seen to be attached by its circumference to a ring of cartilage (_Annulus membranae tympani_; see also p. 26) (_at_); the ring is attached anteriorly and above to the squamosal bone (_sq_), and in the rest of its circumference to the surrounding soft parts, _i.e._ the _M. depressor maxillae_ (_dm_), the _M. temporalis_ (_t_), and their fasciae. In the middle of the membrane is a small, rounded, white part (_col_) which can be traced backwards and upwards towards the circumference.

The membrane consists of fibres of connective-tissue which radiate peripherally from the central point of attachment of the columella; in the peripheral portion unstriated muscular fibres are also found (Leydig).

[Illustration: Fig. 242.

I. The tympanic membrane of _Rana esculenta_; natural size. After Retzius.

II. The tympanum as seen after removing the tympanic membrane; natural size. After Retzius.

_at_ Annulus membranae tympani. _col_ Columella. _ct_ Fissure-like cavity. _dm_ M. depressor maxillae. _mt_ Tympanic membrane. _sq_ Squamosal. _t_ M. temporalis. ]

Internally the tympanic membrane is covered by columnar epithelium, a continuation of the mucous membrane lining the tympanic cavity.

*b.* The *tympanic cavity* (Fig. 242 II) is seen, after removing the tympanic membrane, as a flattened, funnel-shaped cavity. The walls of the cavity are lined with a pigmented mucous membrane, under which the cartilaginous ring (_annulus membranae tympani_) extends internally to form the greater part of the wall of the cavity. The cavity is an elongated oval slit (Fig. 242 II, _ct_), with its longer axis directed from above and in front, downwards and backwards, and leading inwards; it is bounded above, below, and in front by the squamosal, behind by the soft parts; above in the roof is the cartilaginous part of the _columella_. The inner or deeper portion of the tympanic cavity is bounded in front by the squamosal, and by the squamous process of the prootici (_proc. squamosus prootici_) in front and above; internally by the cartilage (primordial-cranium) between the prootic and the exoccipital; behind by the _M. depressor maxillae_. This part of the cavity is rounded and covered with mucous membrane, and has in its roof the bony part of the columella, which covers the _foramen ovale_ (_fenestra ovalis_) by its oval, widened end-piece. This deeper portion of the cavity communicates by a short, wide Eustachian tube with the pharyngo-oral cavity; the tube is wide and is of a rounded oval form in section: anteriorly, externally, and internally it is bounded by the pterygoids, posteriorly by soft parts, in which is embedded the styloid process.

The tympanic cavity can be examined from without after removing the tympanic membrane, or from below by means of the Eustachian tube.

*c.* The *columella auris* (Figs. 12, 243) is described by Retzius as consisting of three portions, of which the middle is bony, the external and internal cartilaginous. Parker divides it into four parts (see pp. 25, 26).

The *extrastapedial* (Fig. 243 _a′_, _a″_) is attached to the middle of the tympanic membrane by the oval surface opposite _a′_, and is attached by the process _a‴_ to the _annulus tympanicus_; this process of Retzius is the *suprastapedial* of Parker.

The *mediostapedial* (Parker), or middle bony piece of Retzius (Figs. 12 _a′_, 243 _b_, _b′_), is narrow externally but widens internally to articulate with the interstapedial. Just before reaching the latter it gives off a process (_b′_), to which are attached a few fibres of striated muscle (_m_).

[Illustration: Fig. 243.

The columella; after Retzius. Magnified eight times.

A. Seen from above. B. Seen from behind.

_a′_ Extrastapedial (Parker). Outer cartilaginous portion attached to middle of tympanic membrane (Retzius). _a″_ Attachment of extrastapedial to mediostapedial. _a‴_ Suprastapedial (Parker). Portion embedded in mucous membrane (Retzius). _b′_ Mediostapedial (Parker). Bony part (Retzius). _b″_ Process of mediostapedial. _c_ Interstapedial (Parker). Inner cartilaginous piece (Retzius). _m_ Insertion of small muscle. ]

The *interstapedial* (Figs. 12 _a_, 243 _c_) is cartilaginous; it is thick with a sharply cut-off, slightly concave end, which is placed against the _fenestra ovalis_. The inner surface of the interstapedial is, however, distinctly larger than the opening of the _fenestra ovalis_, consequently it does not fit in accurately, but is attached to the border of the opening by means of connective-tissue; the margins of the _fenestra ovalis_ are hollowed (Fig. 245 II) so as to form a _fossa fenestrae ovalis_, and it is really to the margin of this fossa that the connective-tissue capsule of the interstapedial is attached.

B. The labyrinth or internal ear is contained in a capsule formed of bone and cartilage.

*a.* The *capsule of the labyrinth* (Fig. 244) is formed of two bones, the prootic and the exoccipital (according to Hasse this includes the opisthotic), which are united by cartilage belonging to the primordial-cranium. The fronto-parietal, squamosal, and parasphenoid take only an indirect part in its formation.

On the whole the anterior half of the capsule is formed by the prootic, and the hinder half by the exoccipital; the cavity has its long axis directed from within and above, downwards and outward; the cavity is comparatively large and rounded, and contains the membranous ear.

Four surfaces can be distinguished: a supero-external, an interno-inferior, an anterior, and a posterior (Retzius).

(1) The *supero-external surface* is divided into two parts by a strong, transverse, bony ridge, the _processus squamosus prootici_. The upper half is concave, is directed upwards and outwards, and is formed by the prootic; it is separated from the anterior surface by a bony ridge, which marks the position of the anterior semicircular canal. Posteriorly and medianly it is separated from the posterior surface by a cartilaginous ridge, running from above, downwards and outwards, which marks the position of the posterior semicircular canal. The cartilaginous hinder root of the _processus squamosus prootici_ arises in the cartilaginous ridge just mentioned, and runs outwards and forwards, covering the external semicircular canal.

[Illustration: Fig. 244.

Antero-posterior section through the capsule of the right labyrinth of _Rana esculenta_; after Retzius. Enlarged five times.

_ac._ Aquaeductus cochleae. _av._ Aquaeductus vestibuli. _cp._ Posterior semicircular canal. _cra._ Canalis rami anterioris acustici. _crp._ Canalis rami posterioris acustici. _fr._ Fenestra rotunda. _fsc._ Fovea sacculi et cochleae. _ft._ Trigeminal foramen. _kn._ Cartilaginous suture. _ol._ Exoccipital. _pr._ Prootic. _ps._ Parasphenoid. ]

The lower half of the supero-external surface (under the _processus squamosus_) is irregularly concave; immediately under the _proc. squamosus_ is a shallow groove in the prootic; it is continued on the exoccipital to the jugular foramen. The remaining part of this surface consists of a rounded cartilage, and is part of the primordial-cranium cartilage between the prootic and the exoccipital; posteriorly it has a small oval aperture, the _foramen ovale_ (_fenestra vestibulare_), which with the groove is covered by the _columella_. Above the aperture the cartilage narrows and is continued to the _processus squamosus_.

(2) The *posterior surface* is directly continuous with the supero-external surface, and is formed by the exoccipital. This surface lies behind the ridge formed by the posterior semicircular canal, it is concave, and has two small apertures, separated by a narrow, bony process, and situated near the jugular foramen; these are the _foramen rotundum_ (_fr._) and the _aquaeductus cochleae_ (_ac._).

(3) The *anterior surface* is altogether bony and formed by the prootic (_pr._); the anterior surface of this part of the wall is continuous with the surface of the cranium, and abuts on to the large trigeminal foramen (_ft._); below it is continuous with the under surface of the cranium, below and externally it articulates with the pterygoid.

(4) The *interno-inferior surface* is as a whole hollowed internally, the upper part being pushed in towards the cranial cavity. It is formed by the prootic anteriorly, by the exoccipital posteriorly, and is completed by the cartilage lying between these bones. In the middle of the upper part of the cartilage is a small oval opening (_av._), the _ap. aquaeductus vestibuli_: about midway between this aperture and the jugular foramen is a second opening in the cartilage (_cra._), the opening of the _canalis rami anterioris (vestibularis) acustici_: a little behind and above this is the opening of the _canalis rami posterioris (cochlearis) acustici_, situated in the exoccipital. The cartilage between the prootic and exoccipital in the lower half of the interno-inferior surface rests on the parasphenoid.

*b.* The *position* of the *soft parts* in the capsule. The large outer, rounded part of the cavity contains the saccule and cochlea (_fovea sacculi et cochleae_) (_fsc._). Above, the cavity is more irregular, and contains the utricle and the _sinus utriculi superior_. In front and externally, imbedded in a deep groove, are the anterior and external ampullae (_fovea ampullae anterioris et amp. externae_); to these are attached the corresponding semicircular canals. The anterior semicircular canal opens above and externally into the canal of the _sinus utriculi superior_; the posterior passes into a groove for the posterior ampulla (_fovea ampullae posterioris_), and opens above and internally into the posterior semicircular canal. The external semicircular canal courses in the _processus squamosus prootici_, the posterior in the cartilage (Fig. 244 _cp_) between the prootic and exoccipital, and the anterior in the prootic. The upper and posterior part of the anterior semicircular canal is imbedded in cartilage, on which rests the parasphenoid.

*c.* The *perilymphatic space* (Fig. 245 I and II). The membranous labyrinth does not occupy the whole space enclosed by the hard parts but is surrounded by the perilymphatic space, which contains the perilymph. The periosteum and perichondrium form the outer lining of the space, and are for the most part pigmented:

The perilymphatic space is widest in the lower part of the organ, in the region of the _fovea sacculi et cochleae_, especially externally and behind (_per_); in front it is much narrower (_per^1_). A little higher, in the region of the _tegmentum vasculosum_, the space is wanting, as the membranous labyrinth is here attached to the periosteum.

Around the utricle and saccule the space is comparatively wide; it is continued into the bony canals and ampullae. In the semicircular canals the space is wider on the concave side than on the convex side, the membranous canals being placed eccentrically, as are also the ampullae, though to a less extent. The periosteum and perichondrium lining this cavity form a very delicate, pigmented membrane, formed of numerous fine elastic fibres which cross each other irregularly; its inner surface is lined with an incomplete layer of branched protoplasmic cells with large oval nuclei. From this membrane numerous irregular bundles of fibres, in the form of trabeculae, pass into the space and form a rich network, which is attached internally to the outer surface of the membranous labyrinth and holds it in position. Free nucleated leucocytes are occasionally met with in the meshes of this network. The perilymphatic space is prolonged into two subsidiary cavities:--

[Illustration: Fig. 245.

The membranous labyrinth of _Rana esculenta_, within its natural covering of periosteum; after Retzius.

I. Seen from the side; magnified ten times.

II. The hinder half; magnified ten times. Seen obliquely from above, and in front, and from the side.

_aa_ Anterior ampulla. _adf_ Apertura fenestrae ovalis. _al._ Apertura lagenae. _ap._ Posterior ampulla. _apb._ Opening into the pars basilaris. _ca_ Anterior semicircular canal. _ce_ External semicircular canal. _cp_ Posterior semicircular canal. _dfo_ Ductus fenestrae ovalis. _dp_ Ductus perilymphaticus. _dp′_ Saccus perilymphaticus. _l._ Lagena cochlea. _ms._ Macula sacculia. _pb_ Pars basilaris cochleae. _per_ Wider part of perilymphatic space. _per^1_ Narrower part of perilymphatic space. _ra._ Ramus anterior. _rn._ Ramulus neglectus. _rp._ Ramus posterior. _rs._ Ramulus sacculi. _s._ Saccule. _sfo_ Saccus fenestrae ovalis. _spl_ Saccus perilymphaticus. _tv_ Tegmentum vasculosum. _u_ Utricle. ]

(1) The *ductus fenestra ovalis* (Retzius), (Fig. 245 _dfo_) commences as an opening (_adf_) immediately opposite the _foramen ovale_ of the hard capsule, which leads into a moderately large canal, the structure under consideration. It passes forwards and outwards through the _fenestra ovalis_ between the interstapedial and the outer wall of the capsule into the oval depression (_fossa fenestrae ovalis_), and rapidly widens to form a short, flattened, blind sac (_saccus fenestrae ovalis_), which is lodged in the fossa (_sfo_). Its walls are thin and pigmented.

[Illustration: Fig. 246.

Part of the outer wall of the perilymphatic space: after Retzius. Vérick’s Syst., Obj. III, Oc. 3.

_per._ Periosteum. _pg._ Perilymphatic network. _zn._ Leucocytes. ]

(2) The *ductus perilymphaticus* (Hasse), (Fig. 245 _dp_) passes above and behind the _ductus fenestrae ovalis_, behind the auditory-nerve, and near the cochlea, then behind and above the _lagena_ to the _aquaeductus cochleae_ (Fig. 244 _ac_), where it forms a short, wide tube, which passes backwards and inwards through this canal to the _canalis jugularis_; here it lies close to the nerves and forms a short oval sac (_saccus perilymphaticus_) (_dp′_), which communicates with the sub-arachnoid space of the cranial cavity by means of a tube from the neck of the sac. The walls of this structure are thin and formed of connective-tissue with very few pigment-cells. The other extremity of the tube passes to the _pars basilaris_ and under the _sinus post. utri._, between it and the _pars neglecta_; it then courses to the outer side of the hinder end of the external semicircular canal: the tube then bends downwards to the outer side of the utricle and saccule to open into the general perilymphatic space.

*d.* The *membranous labyrinth* (Figs. 247, 248) has the following parts: the utricle and _sinus superior_, the _recessus utriculi_, the anterior semicircular canal and anterior ampulla, the external semicircular canal and external ampulla, the posterior semicircular canal and the posterior ampulla, the saccule, _ductus endolymphaticus_, and _saccus endolymphaticus_, the _pars neglecta_, the _lagena cochleae_, the _pars basilaris cochleae_, and the so-called _tegmentum vasculosum_.

In addition the following nerve-terminations can be distinguished: (1) The _macula ac. recessus utriculi_, (2) the three _cristae acusticae ampullorum_, (3) the _macula ac. sacculi_, (4) the _macula ac. neglecta_, (5) the _papilla ac. lagenae cochleae_, and (6) the _papilla ac. basilaris cochleae_.

The auditory nerve divides immediately beyond its origin from the _medulla oblongata_ to form a _ramus anterior_ and a _ramus posterior_, which course alongside each other for a short distance, the latter lying behind and above the former. The _R. anterior_ runs forwards and outwards under the utricle, giving off the _R. sacculi_, which runs downwards and outwards; the _R. rec. utriculi_ is then given off as a number of fibres, which run upwards and forwards; the main nerve then divides to form the _R. ampullae anterioris_ and the _R. ampullae externae_, which course together for a short distance and then separate to reach their respective ampullae. The _R. posterior_ runs backwards and outwards, gives off the _R. lagenae_, and then divides to form the _R. neglectus_, running upwards, the _R. basilaris_ running downwards and backwards, and the _R. ampullae posterioris_ which courses backwards and outwards.

(1) The *utricle* (_utriculus_) (Figs. 247 and 248 _u_) is irregularly cylindrical in form: commencing at the _recessus utriculi_ it passes forwards and outwards; then backwards, inwards, and upwards, to terminate at the _sinus posterior_, where it is slightly contracted. At about its middle it is divided into an anterior and a posterior part by an incomplete, sickle-shaped partition, formed by the posterior semicircular canal opening obliquely into the utricle, and so causing a fold in the posterior wall: on the anterior wall there is no fold; the aperture left in the partition is the _apertura utriculi_.

The posterior part of the utricle receives the _sinus superior_, which is formed by the junction of the two vertical semicircular canals. The anterior part of the utricle receives the hinder dilated end of the external semicircular canal by an opening in its posterior wall, close to the _apertura utriculi_. In the lower wall or floor is the narrow opening leading into the _saccule_ (_canalis utriculo-saccularis_): this opening is placed with its long axis parallel to the long axis of the utricle, with its broader end posterior, and the narrower end anterior.

(2) The *recessus utriculi* (Figs. 247 and 248 _rec_). The anterior end of the utricle widens and curves downwards and outwards to form the _recessus utriculi_; on its floor is a thin, kidney-shaped plate or otoliths, resting on the _macula ac. recessus utriculi_ (_mu_), which receives the _ramulus rec. utriculi_; under it the _ramulus amp. anterioris_ and the _ramulus amp. externae_ run forwards and close together to reach their respective ampullae, which are close together at the antero-external wall of the _recessus utriculi_. The otolith is a glassy, homogeneous plate, with numerous vacuole-like spaces and striated borders; it covers the whole of the _macula_.

[Illustration: Fig. 247.]

[Illustration: Fig. 248.

The right membranous labyrinth of _Rana esculenta_; after Retzius. Magnified 20 times. Fig. 247 seen from the inner side; Fig. 248 seen from the outer side.

_aa_ Anterior ampulla. _ae_ External ampulla. _ap_ Posterior ampulla. _apn_ Apertura partis neglectae. _au_ Apertura utriculi. _ca_ Anterior semicircular canal. _ce_ External semicircular canal. _cp_ Posterior semicircular canal. _cus_ Canalis utriculo-saccularis. _de_ Ductus endolymphaticus. _l_ Lagena cochleae. _mn_ Macula acustica neglecta. _ms_ Macula acustica sacculi. _mu_ Macula acustica recessus utriculi. _pb_ Pars basilaris cochleae. _pl_ Papilla ac. lagenae. _ppb_ Papilla ac. basilaris. _raa_ Ramulus ac. anterioris. _rae_ Ramulus amp. externae. _rap_ Ramulus amp. posterioris. _rb_ Ramulus basilaris. _rec_ Recessus utriculi. _rl_ Ramulus lagenae. _rn_ Ramulus neglectus. _rs_ Ramulus sacculi. _s_ Saccule. _sp_ Sinus utriculi posterior. _ss_ Sinus utriculi superior. _tv_ Tegmentum vasculosum. _u_ Utriculus. ]

(3) The *anterior ampulla* and *semicircular canal* (Figs. 247, 248, _aa_, _ca_). The anterior ampulla is a rounded, oval vesicle, with a depressed roof (Fig. 250 I); on the floor is a transverse low septum, which bears the _crista acustica_ (_cr_) on its free border; seen from above the _crista acustica_ (Fig. 249 II, _aa_, _cr_) has concave borders anteriorly and posteriorly; the ends are broad, rounded, and somewhat raised; and in the middle it presents a small elevation (Fig. 249 _cr_). On the _crista acustica_ rests the _cupula terminalis_ (Fig. 250 I, _cu_); this is arched above but of the same form as the _crista acustica_ below, from which it is separated by an even slit-like space; the ends are not rounded but hollowed out. The substance of the _cupula_ is very soft and has parallel striations, formed of fine fibres and running from above downwards; it separates very easily from the _crista acustica_. The anterior ampulla is directed forwards, outwards, and slightly upwards, to open into the anterior semicircular canal (_canalis m. anterior_) (_ca_), which curves first upwards and forwards, then backwards, inwards, and upwards, to open by means of a slightly dilated end into the _sinus superior utriculi_.

(4) The *external ampulla* and *semicircular canal* (Figs. 247, 248 _ae_, _ce_). The external ampulla lies immediately external to the anterior ampulla; it also is an oval vesicle, and corresponds with the anterior ampulla in size and shape, except that the roof is higher. The roof is directed backwards, the floor forwards; the _septum transversum_ is low, placed vertically, and bears a triangular, slightly depressed _crista acustica_: the broader, rounded end of the _crista_ is directed upwards, the apex downwards. The corresponding _cupula terminalis_ is relatively high, and is of the same shape as the _crista_, and is striated. The external ampulla is continuous with the external semicircular canal (_canalis m. externus_) (_ce_), which courses outwards and backwards; then backwards, inwards, and slightly upwards, touches the roof of the posterior ampulla; then curves forwards and inwards to terminate by a slightly dilated end in the anterior part of the utriculus.

(5) The *posterior ampulla* and *semicircular canal* (Figs. 247, 248, and 249 _ap_, _cp_). The posterior ampulla commences at the posterior end of the _sinus post. utriculi_, and is directed outwards and backwards. It corresponds in all other points with the anterior ampulla. The posterior semicircular canal (_ce_) (_canalis m. post._), into which the ampulla opens, curves upwards, inwards, and forwards, to open into the upper end of the _sinus superior_.

[Illustration: Fig. 249.

The membranous labyrinth of _Rana esculenta_; after Retzius.

I. Part of membranous labyrinth to show relations of the ductus and saccus endolymphaticus to the cochlear part; magnified.

II. The recessus utriculi and the external ampulla; magnified.

III. To show tegmentum vasculosum, pars basilaris, pars neglecta, etc.

IV. To show relations of the cochlear part to the pars neglecta.

_aa._ Ampulla anterior. _ae._ Ampulla externa. _al._ Apertura lagenae. _ap._ Posterior ampulla. _apn_ Apertura partis neglectae. _au._ Apertura utriculi. _ca._ Canalis m. anterior. _ce._ External semicircular canal. _cp._ Posterior semicircular canal. _cpb._ Opening into pars basilaris. _cr._ Crista acustica. _cus._ Canalis utriculo-saccularis. _de._ Ductus endolymphaticus. _dp._ Ductus perilymphaticus. _l._ Lagena cochleae. _ma._ Macula ac. recessus utriculi. _mn._ Macula ac. neglecta. _mp._ Membrana basilaris. _pb._ Pars basilaris cochleae. _pe′._ Dark spot on either side of crest of ampulla. _pl._ Pars ac. lagenae. _pn._ Pars neglecta. _ppb._ Papilla ac. basilaris. _ra._ Ramus anterior. _raa._ Ramulus amp. anterioris. _rae._ Ramulus amp. externa. _rap._ Ramulus amp. posterioris. _rb._ Ramulus basilaris. _rec._ Recussus utriculi. _rl._ Ramulus lagenae. _rn._ Ramulus neglectus. _rp._ Ramus posterior. _rs._ Ramulus sacculi. _s._ Saccule. _sp._ Posterior semicircular canal. _spl._ Saccus perilymphaticus. _ss._ Sinus utriculi superior. _tv._ Tegmentum vasculosum. _u._ Utricle. ]

(6) The *saccule* (_s_), *ductus endolymphaticus* (_de_), and the *saccus endolymphaticus* (Figs. 247, 248, 249). The saccule (_s_) is an oval vesicle, placed under the anterior part of the utricle and directed outwards and downwards; below it is flattened in a direction from in front and within, outwards and backwards; above it is wider. In the inner and anterior surface is the rounded, oval _macula acustica sacculi_ (Figs. 247 and 248 _ms_), to which is distributed the _R. sacculi_ (_rs_) from above; a large otolith rests on the macula and occupies a large portion of the cavity, more especially the lower portion. The tubular _ductus endolymphaticus_ (_de_) arises by a narrow oval opening placed in the upper and inner part of the wall, runs upwards and to the angle between the utricle and the _sinus superior_, continues in the same direction for a short space, and then curves inwards to pierce the _apertura aquaeductus vestibuli_, and so reach the cranial cavity. It then forms a large, thin-walled sac (_saccus endolymphaticus_), placed between the brain and cranium. The sac is very vascular and contains crystalline otoliths.

(7) The *pars neglecta* (Figs. 247, 248, 249) was described by Hasse as the ‘first part of the cochlea’ (‘Anfangstheil der Schnecke’), but according to Retzius it does not belong to the cochlea. It is placed above and in front of the _pars basilaris cochleae_, above and a little behind the _lagena cochleae_, therefore above the upper and posterior part of the saccule, and under the middle part of the utricle. It is really a prolongation of the saccule, with which it communicates by an elongated oval opening placed externally and immediately below the opening of the _canalis utriculo-saccularis_. It is an oval vesicle, with its roof intimately united with the lower wall of the utricle; anteriorly it is broad, posteriorly narrowed. The _macula acustica neglecta_ is attached to the roof of the vesicle and consists of an anterior heart-shaped and a posterior semilunar portion united by a narrow connecting piece (Fig. 250 III and VII). The _ramulus neglectus_ divides into two branches, which supply the two parts of the _macula_. On the _macula acustica neglecta_ rests the _membrana tectoria_ (Deiters); the membrane is S-shaped, with the anterior end narrow, the posterior broad (Fig. 250 VII); the borders of the membrane are pierced by numerous small round holes, the central part has smaller and fewer perforations, and is finely striated. From the middle of the posterior part of the upper surface a thicker portion projects downwards into the cavity of the _pars neglecta_; it has a narrow, deep notch for the nerve at about its middle; anteriorly it points towards a sickle-shaped piece, which is curved inwards. Canals run obliquely downwards and inwards from the apertures on the superior surface. The membrane is clear, homogeneous, partly finely striated, and corresponds with the _membrana tectoria_ of the _pars basilaris_, etc.

(8) The *lagena cochleae* (Figs. 247, 248, and 249 _l_) is an oval swelling of the membranous labyrinth; it lies close to the sacculus with its broader end forwards, the narrower directed backwards. By a large rounded opening at the posterior end it communicates with the saccule by means of a rounded space common to the _lagena cochleae_ and the _cochlea_. The _papilla acustica lagenae_ (_pl_) is situated in the posterior wall of the _lagena_; it is elongated, oval, and supplied by the _ram. lagenae_. The _papilla_ is covered by a plate-like otolith formed of numerous rounded particles.

[Illustration: Fig. 250.

The membranous labyrinth of _Rana esculenta_; after Retzius.

I. Transverse section of the anterior ampulla. Magnified 50 times.

II. Piece from under surface of the cupula from the anterior ampulla. Vérick’s Syst., Obj. VIII. Oc. 3.

III. The macula acustica neglecta, seen from below. Vérick’s Syst., Obj. IV, Oc. 3.

IV. Part of wall of the anterior ampulla.

V. Part of the cochlea, the pars basilaris cut longitudinally. Vérick’s Syst., Obj. I, Oc. 3.

VI. Longitudinal section of the pars basilaris. Vérick’s Syst., Obj. I, Oc. 3.

VII. The macula ac. neglecta, seen from below. Vérick’s Syst., Obj. IV, Oc. 3.

VIII. The pars basilaris, seen from behind and the outer side. Vérick’s Syst., Obj. I, Oc. 3.

IX. Transverse section of the external ampulla. Magnified 175 times.

_apb_ Oval opening into sacculo-cochlear space. _cr_ Crista acustica. _cu_ Cupula terminalis. _dp_ Ductus perilymphaticus. _mb_ Section of thinner wall of pars basilaris. _mt_ Tectorial membrane. _mw_ Thickened membranous wall. _n_ Nerve-fibres. _pb_ Pars basilaris. _pe′_ Area of coarsely granular cells. _ppb_ Papilla acustica basilaris. _r_ Epithelium on raphe. _rb_ Ramulus basilaris. _rn_ Ramulus neglectus. _tv_ Tegmentum vasculosum. ]

(9) The *pars basilaris cochleae* (Figs. 247, 248, and 249 _pb_) is placed on the posterior thickened wall of the saccule and lies above and behind the _lagena_. It forms a small, oval, pocket-like protuberance, with the long axis directed from in front and above, backwards and outwards, its opening being directed forwards and outwards. The short _ram. basilaris_ passes in from above to supply it. The walls of this dilatation are thick and stiff, with the exception of a small portion, the _membrana basilaris_ (Hasse) (_mb_), which closes the opening into a small dilatation on the anterior inner wall. The _ramulus basilaris_ (_rb_) divides into, at least, two branches, and passes close to the _membrana basilaris_ (_mb_), where the elongated and oval _papilla ac. basilaris_ (Fig. 250 _ppb_) is placed. The _papilla_ is covered by a _membrana tectoria_ (Fig. 250 _mt_), which is often found separated from the papilla, probably by the action of the reagents used. The form of this membrane is peculiar but will easily be understood from the figure (Fig. 250 _mt_). In structure it is similar to the corresponding structures found in other parts of the ear.

[Illustration: Fig. 251.

Preparations from the ear of _Rana esculenta_; after Retzius.

I. Part of the membranous wall seen from the surface. Vérick, Obj. VI, Oc. 3.

II. Transverse section of the membranous wall. Vérick, Obj. III, Oc. 3.

III. Epithelium from the neighbourhood of the macula ac. rec. utriculi. Vérick, Obj. III, Oc. 3.

IV. Branched cells from the yellow spot on the floor of the anterior ampulla. Vérick, Obj. III, Oc. 3.

V. Epithelium from the roof of the anterior ampulla. Vérick, Obj. III, Oc. 3.

_re_ Epithelium of raphe. _e_ Pavement epithelium. _pe_ Protoplasmic cells. _pg_ Perilymphatic tissue. ]

(10) The *tegmentum vasculosum* (Deiters) (Figs. 245, 248, and 250 _tv_) is an oval, shell-shaped dilatation of the membranous labyrinth; its long axis is directed from above and in front, downwards and backwards. The walls of the _tegmentum_ are thin and intimately attached to the periosteum.

*e.* The *minute structure* of the membranous labyrinth (Figs. 251 252).

(1) The *walls* of the membranous labyrinth have the same general structure throughout: the walls are usually thicker at the nerve-terminations, in the ampullae, semicircular canals, _pars neglecta_, and especially the _pars basilaris_; the wall of the _tegmentum tympani_ are the thinnest. The walls are transparent, homogeneous, refractive, and, at places, show a faint striation, which is, as a rule, not due to the presence of fibres; in parts of the _recessus utriculi_, and in the outer wall of the _saccule_, especially near the _tegmentum vasculosum_, more or less distinct fibres can be made out. Sections of the wall show spindle-shaped cells, with the processes usually arranged parallel to the surfaces; seen from the surface, the cells are seen to branch in all directions (Fig. 251 I, II). In the thinner parts of the walls the cells are few or altogether absent. The outer surface of the membranous labyrinth is uneven, in consequence of the attachment of the perilymphatic network. Blood-vessels are also attached to the outer surface, and pierce the wall, especially near the nerve-terminations.

The whole of the inner surface is lined with a layer of polygonal, tesselated epithelium-cells. The size and height of the epithelium varies in different parts. On the outer wall of the saccule the cells are large, but on the inner wall small; they are also large in the semicircular canals, except on a small raphe on the inner and outer side, where they are smaller but higher (Fig. 251 _re_); in the ampullae the cells are large, except on the roof. In the utricle and _sinus superior_ they are also moderately large. In addition to the places mentioned, a smaller epithelium is found on the floors of the ampullae, in the _recessus utriculi_, and near all the nerve-terminations and on the sides of the ampullar septa. Surrounding the nerve-terminations of the _macula rec. utriculi_, _macula sacculi_, and _papilla lagenae_ are found narrow, branched, yellowish cells (Fig. 251 _pe_) with spindle-shaped nuclei. Cells of a third kind, first described by Deiters, Hasse, and Kuhn, in the _tegmentum vasculosum_, and in the ampullae by Hasse and Kuhn, are also found in the utricle. They contain a yellowish pigment, and are collected into two sharply differentiated groups in each ampulla (Hasse has one placed before and one behind the septum on the floor). The cells are cylindrical, the upper parts striated, the lower narrower, and the bases again widened to a polygonal, more homogeneous plate, which is fixed to the wall. On the _tegmentum vasculosum_ the corresponding cells are not so high.

(2) The *nerve-terminations*. The larger branches of the auditory nerve contain medullated fibres of various dimensions and bipolar, spindle-shaped ganglion-cells. The nerves pierce the walls obliquely or vertically, and retain their medullary sheaths until near their final distribution. On each of the nerve-terminations is found nerve-epithelium, which varies in height in different parts. In the _crista acustica_ it measures 0.075 mm. in height in the middle part, 0.06 mm. at the sides; on the _macula rec. utriculi_ 0.09 mm., on the _macula sacculi_ 0.075 mm., on the _papilla lagenae_ 0.06 mm., on the _papilla part. basil._ 0.045 mm., on the _macula neglecta_ 0.075 mm. The epithelium is of two kinds, hair-cells and sustentacular cells.

[Illustration: Fig. 252.

The nerve-terminations in the membranous labyrinth of _Rana esculenta_; after Retzius.

I. Vertical section through the crista acustica of the anterior ampulla. Vérick’s Syst., Obj. III, Oc. 3.

II. Vertical section through the macula ac. recessus utriculi. Vérick’s Syst., Obj. VIII, Oc. 3.

III. Three isolated hair-cells from the crista ac. of the anterior ampulla. Vérick’s Syst., Obj. VIII, Oc. 3.

IV. Two isolated sustentacular cells from the crista ac. of the anterior ampulla. Vérick’s Syst., Obj. VIII, Oc. 3.

_cr_ Crista acustica. _cu_ Cupula terminalis. _fz_ Sustentacular cells. _h_ Hairs of hair-cells. _hz_ Hair-cells. _n_ Nerve-fibres. ]

α. The hair-cells (Fig. 252 _hz_) have, on the whole, elongated, flask-like forms, but are not all of the same length (0.024–0.04 mm.). The free ends of the cells are rounded, flattened, and yellowish, and each bears a stiff cilium, which is fixed by a broad base to the cell, and thins out towards its free end: the cilia vary in length; in the ampullae their greatest length is 0.13 mm., on the _macula rec. utriculi_ 0.011 mm., and on the _papilla lagenae_ 0.017 mm. The cells are granular, possess rounded oval nuclei, and are fixed by a fine, narrow process (Fig. 252 _hz_), though they usually seem to be rounded off without possessing a process.

β. The sustentacular cells. Under the hair-cells is a finely granular substance, possessing numerous rounded oval nuclei, which are placed in superimposed rows (Fig. 252 _fz_), the deepest row being placed close together and immediately on the membranous wall. After proper treatment and isolation these nuclei are seen to belong to narrow, elongated cells, which rest by a slightly widened base on the wall, and are continued upwards between the hair-cells to reach the surface of the epithelium, where their upper processes are again slightly widened.

γ. The nerve-fibres (Fig. 252 _n_) lose their medullary coats, ascend towards the epithelium, and frequently divide to form two unequal branches, which ascend to the level of the hair-cells, and curve so as to course horizontally as extremely fine varicose fibrillae; these frequently form a network, of which the exact method of termination has not been made out. In some cases a fine fibril may be traced to the base of a hair-cell, but a direct continuation of the one into the other has not yet been traced.

VI. THE EYE.

(Re-written by the translator.)

The organ of sight, the eyeball (_bulbus oculi_), together with its appendages (_tutamina oculi_), will be described in this chapter.

A. The Eye is flattened on the outer surface, more convex on the inner or deeper surface. Its principal axis is directed from behind, forwards and outwards.

The outer transparent portion of the eyeball is the cornea, which forms the outer boundary of the anterior chamber. The larger, white, opaque, and inner portion is the sclerotic coat, which, together with two deeper tunics, the choroid coat and the retina, enclose the posterior chamber of the eye. The pigmented ring placed behind the cornea is the iris, and the aperture it encloses the pupil. The lens is placed immediately behind the iris. On the inner side the optic nerve pierces the sclerotic to enter the eyeball.

*a.* The *sclerotic coat* (_sclerotica s. sclera_) forms about three-fourths of the surface of the eyeball; posteriorly it is pierced by the optic nerve at a point (_porus opticus_) nearer the temporal side than the nasal. The sclerotic coat consists of fibrous tissue externally, with a layer of hyaline cartilage internally (Helfreich). The fibrous layer is formed of bundles of parallel fibres, which cross each other, chiefly at right angles (Hoffmann). The cartilaginous layer ends just behind the line of insertion of the extrinsic muscle of the eye, and is thickest at the point of entrance of the optic nerve (Helfreich).

[Illustration: Fig. 253.

Endothelium from the inner surface of the sclerotic coat; after Hoffmann. ]

The sclerotic coat is rich in nerve-fibres, which form a close network; the fibres, however, do not unite but form the meshes of the network by simply crossing each at acute angles.

The deeper surface of the sclerotic coat is lined with a layer of large endothelial cells (Hoffmann), (Fig. 253), which form the outer wall of the capsule of Tenon.

*b.* The *cornea* and the *anterior chamber*. The cornea forms about one-fourth of the surface of the eyeball and is directly continuous with the sclerotic. In it five layers can be distinguished: a layer of stratified epithelium or conjunctiva, an anterior hyaline membrane, the true corneal substance, a posterior hyaline membrane, and a layer of endothelium.

(1) The *corneal epithelium* is a layer of stratified epithelium covering the superficial surface of the cornea. The superficial layer forms a beautiful mosaic of polygonal cells; the middle layers are polygonal in all sections, while the deepest layer is more or less columnar. Except in the most superficial layer, all the cells have serrated surfaces. Smaller cells possessing each two nuclei are also found between the columnar cells, and are evidently cells in process of division; according to Waldeyer, cell-proliferation may also take place in the middle layers.

The basal or deeper portions of the columnar cells possess a clear border, which reminds one of the hyaline border found on the free border of columnar epithelium in other parts. The cells are here so closely applied to one another that these borders have the appearance of a continuous, highly refracting membrane (Rollett); according to Henle, the border consists of a network of very fine processes from the cells above.

(2) The *true corneal substance*, and (3) the *anterior hyaline membrane*. The corneal substance consists of flat bundles of fibres arranged in laminae, with cement-substance and connective-tissue corpuscles interposed. The fibrils are extremely fine (0·0001 mm., Engelmann), and bound together into bundles by cement-substance. The bundles of the laminae are arranged at various angles, though many are placed at right angles to each other (Waldeyer).

Between the laminae are flattened spaces, which seen in section are spindle-shaped. By proper treatment they are seen to be irregular, branched spaces, which communicate by fine canals and form part of the Recklinghausen-canals or lymph-system. These spaces contain branched, connective-tissue corpuscles (Toynbee), and a colourless fluid.

The corpuscles (Fig. 254 _e_) do not fill the spaces which they occupy. They possess large nuclei, surrounded by granular protoplasm.

[Illustration: Fig. 254.

Preparation from cornea of _Rana esculenta_; after Klein, Hartnack’s Syst., Obj. VII, Oc. 3.

_a_ Nerve of first order. _b_ Nerve of second order. _c_ Nerve of third order. _d_ Nerve of fourth order. _e_ Corneal corpuscles. ]

The canals by which these spaces communicate (‘Saftcanälchen’ of Recklinghausen) lie, in general, parallel to the surfaces of the cornea, and communicate by joining at acute angles or by short transverse branches. According to Lavdowsky, these canals have a distinct lining membrane.

The anterior hyaline[87] layer (Bowman’s or Reichert’s lamella) is not so well seen in the frog as in some higher animals; it is simply a portion of the corneal substance, of somewhat denser structure than the rest, into which it passes by a gradual transition.

[Footnote 87: Tamanscheff and Schweigger-Seidel consider the anterior and posterior hyaline membranes to be composed of fine fibrils.]

(4) The *posterior hyaline membrane* (Descemet’s membrane) is a highly elastic, very transparent layer, placed behind the true corneal substance; in the frog some few bundles of fibres belonging to the true corneal substance appear to pass into the posterior hyaline layer, although they cannot be traced further through its substance. The structure of the membrane is, in consequence of its transparency, unknown, though the above observation seems to point to a fibrillar origin.

(5) The *corneal endothelium* is a single layer of polygonal cells of 0·02 mm. diameter. The cells possess the power of altering their shape when stimulated (Klebs).

[Illustration: Fig. 255.

Preparation from cornea of _Rana esculenta_; after Klein. Hartnack’s Syst., Obj. X immers., Oc. 3.

_a_ Endothelial cells. _b_ Nuclei of endothelial cells. _c_ Nerves of third order in the tissue of the cornea propria. _d_ Nerves of the fourth order. ]

(6) The *nerves* of the cornea are derived from the _ramus ophthalmica trigemini_; they pierce the sclerotic coat in front of the sclerotic cartilage and then course towards the cornea, at the margin of which they form a coarse network of medullated fibres. From this about thirty nerves pass towards the cornea, which they enter, and then very quickly lose the main part of their medullary sheaths. According to Wolff, a portion of the nerves retain their medullary sheaths, or in some cases appear to regain it after having lost it.

The nerves passing from the plexus (nerves of the first order, Klein) give off smaller branches, which for a short distance have a serpentine or rectilinear course. By a few anastomoses they form a loose plexus (nerves of the second order, Klein). After a longer or shorter course they give off numerous lateral fibres, or terminate in several such fibres arising at one point (nerves of the third order, Klein). These are distinguished by their size, varying only within small limits, and by the possession of more or less regularly placed varicosities; the clearer portions are longitudinally striated as though made up of fibrillae; they have a nearly rectilinear course, and, after a longer or shorter course, turn into a direction which is at right angles to the former one; lastly, they remain for long distances unbranched. These nerves are connected one with another by cross fibres running at right angles to them, and in this way a rectangular trellis-work is formed.

The fibrils (nerves of the fourth order) given off by these nerves form networks around the connective-tissue corpuscles, but no direct connection between nerve and corpuscle has been traced; they always appear to lie on that surface of the corneal corpuscle which is directed towards the superficial surface of the cornea (Klein). In the endothelium covering the membrane of Descemet these fibrils can be traced coursing along the margins of the cells (Fig. 255 _d_), and sometimes undergoing dichotomous division (Klein).

Almost all observers have described these fibrils as possessing varicosities; Hulke, and more recently Wolf, however, deny their presence. Lavdowsky traces nerve-fibrils to the nuclei of the connective-tissue corpuscles.

(7) The *anterior chamber* is the space between the cornea and the iris, and is filled with a watery fluid, the aqueous humour. At the circumference of the chamber are a number of spaces (spaces of Fontana), formed by interruptions in the tissue between the posterior surface of the cornea and the iris; the result is that bands or trabeculae (_ligamentum pectinatum iridis_) pass from the one structure to the other, and between these are the spaces of Fontana.

According to Angelucci these trabeculae are of three kinds: trabeculae passing from the cornea to the iris, formed of connective-tissue; trabeculae from the cornea to the ciliary processes, which contain elastic tissue; trabeculae from the interstitial connective-tissue of the ciliary muscle to the cornea, and formed almost entirely of elastic tissue.

At the junction of the cornea and sclerotic, and just in front of the spaces of Fontana, is a larger and similar space, which may be traced round the whole circumference of the cornea; this, the canal of Schlemm (_Sinus circularis iridis_), is held to be a venous plexus by some observers (Angelucci, and others), according to others it is a lymphatic space in connection with the anterior chamber (Schwalbe, and others). It is certain that the vessels can be very easily injected from the anterior chamber, although a direct communication has not yet been seen.

*c.* The *choroid coat* and the *iris* (_tunica choroidea et iris_, _tunica vasculosa_).

[Illustration: Fig. 256.

The vessels of the choroid and iris; after Hans Virchow.

I. The two roots of the V. bulbi superior. Magnified 10 times. II. Vessels of the iris. Magnified 9 times. III. Origin of the ventral vein. IV. Schema of the choroid vessels; seen from the proximal pole. V. Transverse section through the choroid at the equator. VI. The origin of the choroid arteries from the ophthalmic artery. The greater part of the sclerotic has been removed. Left eye twice natural size. A. From the proximal pole. B. From the temporal side. VII. Part of a choroidal artery attached to the choriocapillaris. Magnified 10 times. VIII. A portion of the choriocapillaris, more highly magnified. IX. The V. ophthalmica and V. bulbi superior on the sclerotic of the right eye. A. Seen from proximal pole. B. Seen from above. Twice natural size.

_A_ Art. ophthalmica. _A′_ Art. choroidea. _An_ R. nasalis of the ophthalmic artery. _At_ R. temporalis of the ophthalmic artery. _ch_ Area of membrana choriocapillaris. _Le_ Outer pigmented layer of choroid. _Li_ Inner pigmented layer of choroid. _N_ Optic nerve. _r_ Vasa recta. _r′_ Transitional part between choriocapillaris and ventral whorl. _r″_ Transitional part between choriocapillaris and upper whorl. _R_ Branches of the circulus iridis major. _Rd_ Distal root of vein of under surface of eye. _Rd′_ Distal root of nasal vein. _Rd″_ Proximal root of nasal vein. _Rp′_ Nasal root of ventral vein. _Rp″_ Temporal root of ventral vein. _Vbs_ V. bulbi superior. _Vh_ V. hyaloidea. _Vo_ V. ophthalmica. _Vp._ Proximal root of vein of under surface of eye. _Vs′_ Nasal root of V. bulbi superior. _Vs″_ Temporal root of V. bulbi superior. ]

*1.* The *choroid coat* lines the deeper surface of the sclerotic coat, but is also prolonged under the cornea to form the iris. The choroid is firmly attached to the sclerotic in two positions, at the point of entrance of the optic nerve, and at the line of junction of the sclerotic and the cornea. Its external surface is closely applied to the deeper surface of the sclerotic, from which it is only separated by a very narrow serous cavity (supra-choroidal space), and to which it is attached by numerous vessels and nerves. The deep surface of the choroid is covered by the retina, to which it is closely attached, except at the ora serrata, the attachment being especially intimate at the _processus ciliares_.

The choroid coat consists of a fibrous layer containing corpuscles and traversed by a very rich vascular anastomosis. The corpuscles of this layer are deeply pigmented, in some cases to such an extent that the oval nucleus cannot be seen; the fibrous tissue is also pigmented, and has consequently a brownish tinge. That portion of the layer immediately below the sclerotic is termed the _lamina fusca_ or _suprachoroidea_, the vessels on the deeper surface forming the _membrana choriocapillaris_. This again is lined on its deeper surface by a hyaline membrane.

α. The arteries (Fig. 256 VI; VII, VIII) supplying this coat are two branches of the _arteria ophthalmica_; these form a capillary network (Fig. 256 VII) resembling the corresponding structure found in mammals. The meshes have approximately the same size, while the capillaries themselves vary considerably in size. This network is, however, only complete on the nasal, temporal, and proximal part of the upper surfaces. Towards the _corpus ciliare_ the meshes become wider and elongated; the capillaries then unite at acute angles parallel with the longitudinal axis of the eye. The network (_choriocapillaris_) exists in a simple layer within the two arteries which form it, and superficial to the veins (Virchow).

β. The veins of the choroid (Fig. 256 III, IV, IX) are (1) a vein which unites at the lowest point of the equator of the eye with the _V. hyaloidea_ to form (2) the _V. ophthalmica_, two small branches of the _V. bulbi superior_, which unite outside the sclerotic, and (3) the _vasa recta_.

(1) The larger vein arises from the greater part of the under surface of the eye; it gives off branches to each side, which radiate to form a ‘whorl’ or star-shaped capillary anastomosis (Fig. 256 III), the two halves of which have no connection. A proximal and a distal root can be distinguished in the anastomosis; the distal lies towards the _corpus ciliare_, and occupies exactly one-fourth of the circumference of the choroid at its junction with the _corpus ciliare_.

(2) The two branches of the _V. bulbi superior_ lie alongside the _corpus ciliare_ on the upper surface, and each occupies one-fourth of the circumference; they form a similar though simpler figure (Fig. 256 I) to the foregoing, each forming one half.

(3) The _vasa recta_ are numerous parallel vessels which arise in the iris, and coursing centrally empty themselves into the branches of the _V. bulbi superior_ on the superior surface, and into the branches of the venous capillaries on the inferior surface.

*2.* The *iris* is covered anteriorly by a layer of endothelium, continuous with that covering the posterior surface of the cornea, and of similar character. The border of the pupil (_margo pupillaris_) is of a golden colour, outside this bright ring to its outer margin (_margo ciliaris_) the iris is black; the golden colour is due to the presence of cells containing a pale yellow pigment; the nuclei of these cells are round and granular; the cells themselves have rounded outlines (Hoffmann). The black portion of the iris contains more irregular, spindle-shaped cells, with round nuclei, which are hidden by a dense mass of pigment-granules (Iwanoff and Hoffmann).

The true substance of the iris consists of muscle, nerves, blood-vessels, and a connective-tissue stroma, but on the posterior surface is another layer of black, pigmented cells, and this is again covered with a hyaline membrane, in which, however, a fibrous structure may be made out (Koganeï).

The muscle-fibres are long, spindle-cells, which are abruptly swollen in the middle, where the nuclei are situated; the nucleus is oval, 0.009–0.0012 mm. in length, 0.0025 mm. broad, and occupies nearly the whole of the swollen part of the cell (Hoffmann, Grünhagen).

According to Koganeï the iris possesses a _M. constrictor iridis_ (_l. c._ Berlin Sitzungsber.), but no _M. dilatator iridis_; in a former publication (_l. c._ Arch. mik. Anat.) he was unable to find any muscular fibre, and holds the muscle-fibres of Grünhagen to be connective-tissue elements.

The stroma consists of delicate connective-tissue fibrils, enclosing a very large number of pigmented, branched cells.

α. The *arteries* of the iris (Fig. 256 II) arise from an arch (see Vessels of Eye) formed by the _A. ophthalmica_ in the _corpus ciliare_. It commences between the ventral and temporal surfaces by two branches: one courses along the temporal border, the other along the nasal, to meet each other on the nasal surface; the former courses through one-third, the latter embraces two-thirds of the circumference at the iris.

The temporal artery courses along the ciliary border during the first third of its course, it then gradually approaches the border of the pupil; the nasal artery runs at once towards the pupil. On the nasal border of the pupil they anastomose by their branches, and so form a _circulus iridis major_.

Except near their termination, no small vessels arise from this arterial circle; in Fig. 256 II, for example, only five larger branches are given off, three from the temporal side and two from the nasal. The five large branches run towards the circumferential border of the iris and break up into numerous vessels, which form a very irregular and open network. From this network arise the _vasa recta_ already described.

*d.* The *lens* is almost spherical, and is composed of cellular elements enclosed in a capsule (_capsula lentis_).

The capsule is a homogeneous, transparent, structureless, and highly elastic membrane. The deeper surface of the anterior capsule is lined with a simple layer of regular nucleated six-sided epithelial cells.

The lens itself consists of long, flat fibres; seen from the surface these are broad, narrow edge-wise, and in section six-sided prisms. Those lying parallel to the anterior and posterior surfaces are broad and thicker, those towards the border are narrower. These cells are striated, both longitudinally and transversely (Arnold). The cells near the margin, however, have no transverse striation (Hoffmann). The cells of the central parts form a much closer and firmer structure than those at the periphery (Arnold). The peripheral cells are nucleated, and sometimes even possess two nuclei to one cell; the central cells have no nuclei (Arnold).

The cells are held together by a cement-substance and by their serrated surfaces; the serrations are the cause of the transverse striations. The fibres of the lens have a simple arrangement: commencing at the middle point or pole of one surface they pass over the equator to the opposite pole; consequently the long borders of adjacent cells are in juxtaposition, and their pointed extremities meet at points in the axis of the lens (Hoffmann).

Ritter has described short, nucleated cells in the centre of the lens; these are held by Babuchin to be cells which have been arrested in their development.

[Illustration: Fig. 257.

Fibres from the lens of the frog; after Hoffmann. Magnified 700 times. ]

*e.* The *retina* is the innermost coat of the eye; in the recent state it is pale, soft, and smooth. The structures composing it are arranged in ten layers; from the deeper surface towards the choroid these are: the internal limiting membrane, the optic-fibre layer, the ganglion layer, the inner molecular layer, the inner nuclear layer, the outer molecular layer, the outer nuclear layer, the external limiting membrane, the layer of rods and cones, and the pigment layer.

These layers are held together by connective-tissue elements.

(1) The *internal limiting membrane* (_Membrana limitans interna_) will be described together with the connective-tissue elements (10).

(2) The *optic-fibre layer* is formed by the fibres of the optic nerve. The nerve-fibres in their course towards the eye are possessed of medullary sheaths, but on piercing the sclerotic these sheaths are lost. The fibres are now pale, non-medullated, and of very varying thickness. In the mass of fibres nothing can be seen except an extremely fine fibrillation and very fine varicosities; the latter, however, appear to be artificial productions (Hoffmann). This layer of fibres extends over the inner surface of the retina, and gradually thins from the point of entrance of the optic nerve to the limits of the retina.

(3) The *ganglion-layer* lies immediately without the nerve-fibre layer (Fig. 258 _b_). The ganglion-cells are small and usually pear-shaped. The cells possess large nuclei, round which is a thin layer of very granular protoplasm. The cells have inner and outer processes; the inner pass into the nerve-fibre layer, the outer into the inner molecular layer in more or less radiating directions. Manz claims to have traced a direct connection between the inner processes and the fibres of the nerve-fibre layer.

Each ganglion-cell, whatever its shape or size, has only one inner process, which is easily distinguished from the outer process by its being more glistening, by the possession of varicosities, and because this process never branches.

The outer processes are single (Schwalbe) or rarely double (Hoffmann), and have as a rule a direction at right angles to the inner processes. Each outer process is finely granular, which suggests rather a prolongation of the cell-substance than a true process. Frequently they are branched, sometimes forming two equal sized processes, which give off finer twigs; at other times they appear to pass through the whole of the inner molecular layer without undergoing division (Schwalbe). The processes do not inosculate (Santi Sirena).

[Illustration: Fig. 258.

Vertical section through retina of frog; after Hoffmann. Magnified 500 times.

_a_ Internal limiting membrane. _b_ Ganglion-cell layer. _c_ Internal molecular layer. _d_ Internal nuclear layer. _e_ External molecular layer. _f_ External nuclear layer. _g_ Layer of rods and cones. _h_ Pigmented epithelium layer. 1. Inner segments of rods and cones. 2. Outer segments of rods and cones. 3. Outer transparent segments of pigmented epithelium. ]

(4) The *inner molecular layer* (Fig. 258 _c_) is 0·07–0·08 mm. thick (Hoffmann), and consists of a finely granular mass together with the outer processes of the ganglion-layer, and connective-tissue elements.

The granular matter consists of an extremely fine network or reticulum, through which numerous fine fibres course (Schultze, Kölliker, Manz, Heinemann, and others); according to Schultze the supposed molecules or granules of others (Henle, Merkel, and Retzius) are simply the fine meshes of this reticulum. The branched, outer processes of the ganglion-cells form a rich anastomosis in this layer.

(5) The *inner nuclear layer* (Fig. 258 _d_) contains parts of two kinds of cellular elements; these are radial nerve-fibres with large nuclei, and connective-tissue elements (see below, par. 10). The nerve-fibres are easily distinguished by their spindle-shaped varicosities; both cellular elements possess large oval nuclei. The bodies of the cells surrounding the nerve nuclei are almost filled by the nuclei, which have sharply-defined, rounded nucleoli. The fibres to which these cells are attached may be distinguished as inner and outer processes; the inner process is fine, irregularly varicose, and unbranched; the outer process is thicker, finely granular, and is not varicose (Schwalbe). At the margin of the outer molecular layer the outer processes divide, usually into two branches, and at an acute angle to each other, though sometimes at a right angle. The further course of these branches in the outer molecular layer is unknown.

(6) The *outer molecular layer* (Fig. 258 _e_) corresponds in general with the inner molecular layer as regards its structure; it is, however, much thinner.

(7 and 9) The *outer nuclear layer* and the *layer of rods and cones* (Figs. 258 _f_, _g_, 259). The rods and cones are intimately connected with the elements of the outer nuclear layer, hence the two layers are best described together.

The rods (_bacilli_) have two parts or limbs, an outer and an inner, which differ in structure, and in chemical and physical characters. The outer part is highly refractive, the inner more homogeneous and less refractive, the two parts being sharply differentiated from one another.

The outer part is also weakly doubly refracting, the inner has no trace of this property. The rods are 0·05–0·06 mm. in length, of which 0·035–0·04 mm. belongs to the inner limb. The outer end of the outer limb is more or less rounded; the whole has a longitudinal striation (Schultze), due to its being composed of rounded fibrils, about twenty-four to each rod (Hensen). The fibrils are sharply differentiated from each other and have a slightly spiral course; when seen in transverse section these outer limbs do not appear to be round (Schultze), although others hold them to be perfectly rounded (Hoffmann and others), and that the loss of the cylindrical form is due to the methods of treatment. According to Merkel the longitudinal striation is caused by a canalisation of the outer limb, which according to him encloses the processes of the pigmented epithelial layer; he is also of opinion that the spiral appearance is an artificial product. In the latter opinion he is probably wrong, as perfectly fresh rods examined in aqueous humour show the same spiral appearance (Hoffmann): against the canalisation view others observe that the longitudinal striation is most distinct near the inner limit of the outer limb, and that it is impossible to conceive that the processes of the pigment-cells should terminate with such extremely regular ends (Hoffmann).

[Illustration: Fig. 259.

Various preparations from the eye of the frog: chiefly from the retina.

1. Rod from retina in aqueous humour, showing spiral striation. 2. Three rods and one cone after treatment with osmic acid. 3, 4, 5. Rods examined in recent state. 6, 7. Inner segments of two rods after treatment with osmic acid. _a_ Outer limb. _b_ Inner limb. _c_ Lenticular body. _d_ Nucleus of outer nuclear layer. _e_ External limiting membrane. 8. Nuclear body from inner nuclear layer. 9. Twin-cone. 10. Sustentacular fibre of retina. 11. Surface view of pigmented epithelium of retina. 12, 13. Isolated pigmented cells of retina. 14. Four pigmented cells, rods and cones, external limiting membrane, and part of outer nuclear layer attached. 15. Two pigmented cells; each showing three attached rods. 16. Muscle-fibre from the iris.

Figs. 1, 2, 3, 4, 5, 6, 7, 8, 9 are magnified 500 times. Fig. 10, 300 times. Fig. 16, 400 times. All are copied from Hoffmann’s figures.

Figs. 12, 13, 14, 15 are copied from Morano’s figures; Hartnack, Oc. II, Obj. 9. ]

In the central part of the inner end of the outer limb is seen a dark point when the structures are examined in transverse section (Ritter, Manz, Schiess, Schultze, and others). The cause of this is not clearly understood; some hold it to be a fibre (Ritter’s fibres), others hold it to be an artificial product (Hensen).

After treatment with certain reagents the outer limbs show a transverse striation, which is probably produced by the action of these reagents on the sheath of the outer limbs; that a sheath is present is proved by its possession of a different refractive index (Zenker, Schultze) to the rest of the outer limb, and this transverse striation is not seen until the whole organ has undergone considerable _post-mortem_ changes (Hoffmann). Should this change be allowed to proceed a stage further, the outer limbs of the rods split transversely and form small discs from 0·0005–0·00055 mm. thick; this takes place in the outer limb only.

The inner segments of the rods (Figs. 258, 259) are short (0·020–0·022 mm.) and of the same thickness as the outer limbs. When perfectly fresh they appear homogeneous; very quickly changes commence, which are probably due to coagulation. A plano-convex figure (Fig. 259) is then seen at the outer portion of the segment (lens-shaped figure of Schultze); with staining reagents it gives the same reactions as the outer segment of the rods. The rest of this segment forms a short cylinder, which probably has no distinct sheath (Hoffmann, Merkel); some observers are inclined to think that a sheath exists (Landolt, Schwalbe).

The outer segments of the rods are of two chief sizes (Schwalbe). Those of the one kind are large; the second variety occurs less frequently, and the segments are shorter, measuring only 0·002 to 0·0025 mm. The inner segment is a long, thread-like process, except where it is swollen to enclose the lens-shaped body.

The rods are much more numerous than the cones, except at one small spot (_macula lutea_) on the posterior surface of the retina, where only cones are found (Krause).

The cones (_coni_) have each two segments like the rods (Figs. 258, 259). The outer segments are short (4–5 µ), they are slightly conical and terminate externally in a blunt point; they possess a longitudinal striation (Schultze), and very easily break up transversely into small discs, which, however, do not separate so completely as in the case of the rods, in consequence of the presence of a sheath continuous with a sheath on the inner segment.

The inner segments (Figs. 258, 259) have convex sides and measure 12–14 µ; like the corresponding parts of the rods they possess lens-shaped bodies at their junction with the outer segments, but the bodies differ in shape, being bi-convex or rather oval in form. The inner segments are enclosed in a delicate sheath continuous with that of the outer segments.

In some cases two cones are united to form a twin-cone; in such cases the one is always larger than the other (Fig. 259 9), and has several peculiarities which distinguish it from the smaller.

The smaller or secondary member of a twin-cone is longer, and possesses a lens-shaped body which is plano-convex. The larger or principal member of a twin-cone is shorter, has a plano-convex body, but also an oval, homogeneous, glistening body, which is directly attached to the plano-convex body. The shape of the two members is also different.

The *outer nuclear layer* (Fig. 258 _f_) is 14–16 µ thick; the nuclei lie in two layers. The nuclei belonging to rods and cones have the same characters, each nucleus being a large, oval, hyaline body, and enclosing a bright nucleolus. Each nucleus is surrounded by an extremely thin layer of finely granular matter. The inner processes of the nuclear bodies both of the rods and the cones extend to the outer molecular layer, are there dilated and serrated, where they become attached to the outer molecular layer (Schultze, Hoffmann). In some cases, however, the inner process of the nuclear bodies, belonging to the rods, forms only a short fine fibre.

In the case of twin-cones the corresponding parts in the outer nuclear layer possess two nuclei (Schultze).

(8) The *pigment layer* (Figs. 258 _h_, and 259 11, 12, 13, 14, 15) is not intimately attached to the rest of the retina. It consists of cylindrical cells in which two parts or segments are sharply differentiated; the external part, directed towards the choroid coat, is of pale, or colourless granular protoplasm, and occupies one-third of the length of the cell; this part encloses a large, round, nucleolated nucleus. This colourless segment of the cell also includes one or two bright yellow, fat globules (Morano). Seen from the surface the cells are hexagonal (Fig. 259 11). The remaining two-thirds of the cells consists of a brush formed of numerous fine pigmented processes; the ultimate terminations of the processes, which lie parallel to each other, are frequently unpigmented; each cell possesses thirty to forty such processes (Morano).

The processes extend between the rods and cones as far as the external limiting membrane (Figs. 258, 259), or sometimes a little further (Merkel, Morano, Hoffmann). The processes from one pigment-cell surround a number of rods and cones; according to Morano twelve to fifteen rods and cones may be encased or surrounded by the processes of a single cell.

The thickness of this layer varies from 60–70 µ; the nuclei of the cells have a diameter of 10–12 µ, the width of a single cell is from 20–25 µ (Hoffmann).

(10) The *connective-tissue elements* of the retina and the *external* and *internal limiting membranes*. The elements of the retina are supported by connective-tissue elements or sustentacular cells, which have a radial arrangement, and which form the two limiting membranes (Müller).

Each sustentacular cell (Fig. 259 10) has two segments, an inner and an outer, the boundary between these lying in the inner nuclear layer, and being marked by the presence of a large oval nucleus. The inner segment of each cell terminates internally in a wide ‘foot’ or base, or may form several such after having undergone division (Schultze): these bases together form a transparent, thin membrane, the internal limiting membrane (_membrana limitans interna_).

Within the ganglion-layer these cells possess peculiar appendages, which fit round the ganglion-cells and support them (Schwalbe).

The outer segments of the sustentacular cells extend into the outer molecular layer, and then break up into irregular processes which extend radially to the external limiting membrane, and which they probably form. The external limiting membrane (_membrana limitans externa_) is therefore a membrane corresponding to the internal limiting membrane, and formed by the flattened ends of the processes belonging to the sustentacular cells.

The sustentacular cells have a distinct, resistant cell-wall (Schwalbe); the cell-contents are a finely granular protoplasm, and a large oval, nucleated nucleus placed in the inner nuclear layer.

*f.* The *ciliary processes* have the same structure as the rest of the choroid coat: the vessels form more or less longitudinal meshes and are more irregular than in the rest of the choroid.

*g.* The *posterior chamber* and *vitreous body* (Fig. 260). The vitreous humour occupies the greater portion of the cavity of the eyeball, _i.e._ the posterior chamber. The humour consists of a mass of cells enclosed in a transparent hyaloid membrane (_membrana hyaloidea_), which is in contact with the internal limiting membrane of the retina.

The cells forming this structure are small, flattened, transparent, and nucleated (Iwanoff and Virchow); according to the former observer the cells have contractile powers.

The hyaloid membrane is described as structureless by Schwalbe, as fibrous by Pappenheim, Bowman, and Fuikbeiner.

The vessels of the vitreous body (Fig. 260) are as follows. The _A. hyaloidea_ arises at the lowest point of the _corpus ciliare_; it almost immediately divides into two branches, which form a ring at a distance of about 0·5 mm. from the lens and lying on the surface of the vitreous body (Fig. 260 I, II). One, _R. nasalis_, passes to the nasal side and courses through one-fourth of the circle; the other, _R. temporalis_, courses through three-fourths of the circle. The branches are all given off proximally and at right angles to the circle (Fig. 260 I, II). From the _R. nasalis_ only one branch arises, from the _R. temporalis_ seven, the first of which corresponds in point of origin with the branch from the _R. nasalis_. The branches on the nasal and temporal surfaces of the vitreous body are the shortest.

[Illustration: Fig. 260.

The vessels of the vitreous body; after Hans Virchow.

I. Vessels of the vitreous body; seen from the deeper pole and slightly from above. Magnified 6 times.

II. Arteries of the vitreous body of the right eye.

_A_ Seen from the proximal pole. _B_ Seen from the nasal side.

III. Veins of the vitreous body of the left eye.

_A_ Seen from the proximal pole. _B_ Seen from the nasal side.

_a_ Nasal vein. _b_ Temporal vein. _c_ Branch (constant) of temporal vein. _n_ R. nasalis of the ophthalmic artery. _t_ R. temporalis of the ophthalmic artery. _t′_ Termination of the R. temporalis. _V_ Ventral vein. ]

These branches form a capillary network (Fig. 260 I) with elongated meshes, formed by the capillaries anastomosing at acute angles. The capillary network is more dense towards the middle of the proximal surface than in other parts.

The veins arising from this network are three in number (Fig. 260 III); two of these accompany the arteries from their origin, and form a somewhat similar circle around the lens, while the third passes backwards along the ventral surface of the vitreous body to the _papilla nervi optici_. The nasal vein, however, takes a more proximal course than the corresponding artery, the branches of which it crosses; consequently the venous ring is not so perfect as the arterial. The nasal vein is larger and the temporal vein smaller than the corresponding arteries.

The ventral vein is formed near the _papilla nervi optici_ by the union of two smaller branches. The capillary system of these vessels has the usual structure of capillaries, the cells being united by cement-substance (Zimmermann).

The blood-vessels of the vitreous body are accompanied by lymphatics; according to Iwanoff they completely enclose the capillaries: Zimmerman contradicts this view, as he has been unable to find lymphatics on that side of the capillaries directed towards the vitreous body.

B. Appendages of the eye.

The appendages of the eye are the eye-muscles (see pp. 55–59), the eyelids, the Harderian gland, and the lachrymal duct.

*a.* The *eyelids* are two in number, an upper and a lower. The upper eyelid is intimately attached to the eyeball and follows the movements of that organ.

The *lower eyelid* (_membrana nictitans_) is much larger than the upper and has the same functions as the lower eyelid of higher vertebrates. It forms a transparent covering for the eyeball, and is raised by a special muscle (see p. 58); functionally it takes the place of both eyelids of higher vertebrates.

The lower eyelid is a prolongation of the skin, but has only a few pigment-cells, except at its free margin, and no serous glands. Mucous glands are found in two or three rows, closely applied to one another, on the superficial surface of the lid; on the deeper surface they are wanting. The stroma of the lid, like the cutis, is of connective-tissue.

Nerve-fibres can be traced in all directions through the substance of the lid, forming a wide-meshed plexus. Around each gland the plexus becomes finer and by numerous branchings much closer; from the plexus twigs are given off, which divide to form a number of fibrils traceable into the epithelial cells of the glands (Openchowski).

The vessels of the lower eyelid have been investigated by Stricker, (_l. c._); according to him they possess some interesting peculiarities. Many of these capillaries course within a lymphatic vessel, in some places the capillary being contracted by a projection from its inner wall; where this is found the accompanying lymphatic is correspondingly dilated. Such points are especially met with where the capillaries branch; in many cases the capillary was contracted to such an extent that the blood-corpuscles were unable to pass the obstruction. Stricker further observed in the living tissue that such constrictions could take place in a part which a short time previously had been comparatively wide and dilated; further, that many of the nerves were enclosed in similar lymphatics. Langer, however (_l. c._), describes the vessels as being accompanied by an irregular network of small lymphatic vessels.

[Illustration: Fig. 261.

Preparations from the nictitating membrane of _Rana esculenta_ to show distribution of nerves.

I. Preparation of the nictitating membrane to show nervous supply to a capillary vessel; after Klein. Hartnack, Oc. III, Obj. 8.

_a_ Capillary vessel. _b_ Blood-corpuscles. _c_ and _d_ Non-medullated nerve-fibres.

II. To show distribution of nerves in the epithelium; after Klein. Hartnack, Oc. IV, Obj. 8.

_a_} Subepithelial _b_} nerve-fibres. _c_ Fine fibrils between the deepest epithelial cells. _d_ Deepest epithelial cells. ]

The distribution of the nerves in the lower eyelid has been described by Klein. In the epithelium they form a network resembling that found in the cornea (Fig. 261 II); along the blood-vessels the fine fibrils form a perivascular network, which supplies fine twigs to the walls of the vessels (Fig. 261 I). He distinguishes three kinds of pigmented cells.

*b.* The *Harderian gland* is situated at the inner angle of the eye, and is pear-shaped in form. It consists of a number of racemose glands held together by connective-tissue, the whole being enclosed in a relatively thick and strong capsule of connective-tissue.

The alveoli have a diameter of 0·040–0·060 mm.: they possess a lining of epithelium and a lumen which varies considerably in size. The epithelial layer is bounded externally by a membrana propria. The cells are placed eccentrically, they are cylindrical, and composed of finely granular protoplasm; each cell contains a pale, rounded nucleus. The ducts of the alveoli are lined with a single layer of cylindrical epithelium, the cells of which are usually shorter and narrower than those of the epithelium of the alveoli; the ducts open into a single main tube, lined with similar epithelium but strengthened externally by a layer of connective-tissue. The glands secrete a fluid which moistens the free surface of the eye.

The Harderian glands are surrounded by a rich capillary anastomosis which completely invests the alveoli.

*c.* The *lachrymal duct* opens behind and below into the nasal cavity (see p. 389), anteriorly it can be traced forwards, as a small tube imbedded in connective-tissue and lying immediately beneath the skin, to the outer angle of the eye, where it opens by numerous tubules.

The lachrymal duct is lined with ciliated columnar epithelium.

ADDENDA.

HISTOLOGY OF MUSCLE, CARTILAGE, BONE, AND THE CONNECTIVE TISSUES.

LITERATURE.

I. MUSCLE AND NERVE-ENDINGS IN MUSCLE.

*Arnold, J.*, Gewebe der organischen Muskeln. Stricker’s Gewebelehre, 1871. Vol. I, p. 142.

*Arnold, J.*, Ueber die Abscheidung des indigschwefelsauren Natrons im Muskelgewebe. Virchow’s Arch. Vol. LXXI, p. 1.

*Babuchin*, Ueber den feineren und Ursprung des Axencylinders. Centralbl. f. med. Wiss. 1868, p. 755.

*Barfurth, D.*, Die Rückbildung des Froschlarvenschwanzes und die sogenannten Sarkoplasten. Arch. f. mik. Anat. 1887. Vol. XXIX, p. 35.

*Biedermann, W.*, Zur Lehre vom Bau der quergestreiften Muskelfaser. Wiener Sitzungsber. 1876. Vol. LXXIV, Pt. III, pp. 49–62.

*v. Biesiadecki, A.*, and *Herzig, A.*, Die verschiedenen Formen der quergestreiften Muskelfasern. Wiener Sitzungsber. 1859, Vol. XXXIII, p. 146: and in Moleschott’s Untersuchungen, 1860, Vol. VI, p. 105.

*du Bois-Reymond, E.*, Ueber facettenförmige Endigung der Muskelbündel. Berlin. Acad. Monatsber. 1872, pp. 791–814. Abstract in Centralbl. f. d. med. Wiss. 1873. No. 55, p. 868.

*Bowman.* On the minute structure and movements of voluntary muscle. Phil. Trans. 1840, p. 457.

*Bremer, L.*, Ueber die Endigungen der markbaltigen und marklosen Nerven im quergestreiften Muskel. Arch. f. mik. Anat. 1882. Vol. XXI, p. 165.

*Bremer, L.*, Ueber die Muskelspindeln nebst Bemerkungen über Structur, Neubildung, und Innervation der quergestreiften Muskelfaser. Arch. f. mik. Anat. 1883. Vol. XXII, p. 318.

*Calberla, E.*, Studien über die Entwicklung der quergestreiften Muskeln und Nerven der Amphibien und Reptilien. Arch. f. mik. Anat. 1875. Vol. XI, p. 442.

*Calberla, E.*, Ueber die Endigungsweise der Nerven in den quergestreiften Muskeln der Amphibien. Dissert. Freiburg i. B. 1874; also in Zeitschr. f. d. wiss. Zool. 1874. Vol. XXIV, pp. 164–178.

*Chittenden, R. H.*, Histochemische Untersuchungen über das Sarkolemm und einige verwandte Membranen. Untersuch. d. physiol. Instituts d. Universität Heidelberg. Vol. III.

*Cohnheim, J.*, Ueber die Endigung der Muskelnerven. Centralbl. f. d. med. Wiss. 1863, p. 865.

*Eberth, C. J.*, Untersuchungen über die normale und pathologische Leber. Virchow’s Arch. 1864. Vol. XXXIX, p. 74.

*Engelmann, T. W.*, Zur Lehre von der Nervenendigung im Muskel. Jenaische Zeitschr. 1868. Vol. IV, p. 307.

*Engelmann, T. W.*, Untersuchungen über den Zusammenh. von Nerven u. Muskelfasern. Leipzig, 1863.

*Engelmann, T. W.*, Microscopische Untersuchungen über die quergestreifte Muskelsubstanz. Pflüger’s Arch. 1873. Vol. VII, pp. 33–71, and pp. 155–187.

*Engelmann, T. W.*, Ueber die Endigung der motorischen Nerven in den quergestreiften Muskeln der Wirbelthiere. Centralbl. f. med. Wiss. 1863, p. 289.

*Ewald, A.*, Ueber die Endigung der motorischen Nerven in den quergestreiften Muskeln. Pflüer’s Arch. 1876. Vol. XII, p. 529.

*Ewald, A.*, and *Kühne, W.*, Die Verdauung als histologische Methode. Heidelb. naturhistor.-med. Verhandl. 1877. Vol. I, p. 451.

*Exner, S.*, Notiz zu der Frage von der Faserverteilung mehrerer Nerven in einem Muskel. Pflüger’s Arch. 1885. Vol. XXXVI, p. 572.

*Fischer, E.*, Ueber die Endigung der Nerven im quergestreiften Muskel der Wirbelthiere. Arch. f. mikrosk. Anat. 1877. Vol. XIII, p. 365.

*Froriep, A.*, Ueber das Sarcolemm und die Muskelkerne. Arch. f. Anat. u. Physiol. 1878, p. 416.

*Gerlach, J.*, Ueber das Verhalten der Nerven in den quergestreiften Muskelfäden der Wirbelthiere. Sitzungsb. Erlangen. 1873. Vol. V, p. 97; Abstract in Centralbl. f. d. med. Wiss. 1874, p. 227.

*Gerlach, J.*, Das Verhältniss der Nerven zu den willkürlichen Muskeln der Wirbelthiere. Leipzig, 1874.

*Gerlach, J.*, Ueber das Verhältniss der nervösen und contractilen Substanz des quergestreiften Muskels. Arch. f. mik. Anat. 1877. Vol. XIII, p. 399.

*Golgi, C.*, Sui Nervi dei Tendini dell’ Uomo e di altri Vertebrati e di un nuovo Organo Nervoso terminale Musculo-tendineo. Torino. Estr. dalle Memorie della Reale Acc. di Torino. Series II. 1880, Vol. XXXII.

*Grützner, P.*, Zur Anatomie und Physiologie der quergestreiften Muskeln. Recueil Zoolog. Suisse, 1884. Vol. I, pp. 665–684.

*Haycraft, J. B.*, Upon the cause of the striation of voluntary muscular tissue. Quart. Journ. Micros. Soc. 1881. Vol. XXI, p. 307.

*Hensche*, Ueber die Drüsen und glatten Muskeln in der äusseren Haut von Rana temporaria. Zeitschr. f. wiss. Zool. 1856. Vol. VII, p. 273.

*Hensen, V.*, Ueber die Entwicklung des Gewebes und der Nerven im Schwanze der Froschlarve. Virchow’s Arch. 1864. Vol. XXX, p. 51.

*Jakimovitsch*, Ueber die Regeneration der glatten Muskelfasern. Centralbl. f. d. med. Wiss. 1879, p. 897.

*Key, A.*, Bidrag till Nervernas ändningsätt i Musklerna. Förhandlingar vid Skandinaviska Naturforskaemötet i Stockholm, 1863. Abstract in Centralbl. f. d. med. Wiss. 1866, p. 212. (Muscles of frog’s tongue.)

*Klebs, E.*, Die Nerven der organischen Muskeln. Centralbl. f. d. med. Wiss. 1863, p. 561.

*Klebs, E.*, Die Nerven der organischen Muskeln. Virchow’s Arch. 1865. Vol. XXXII, pp. 169–198.

*v. Kölliker, A.*, Gewebelehre.

*v. Kölliker, A.*, Einige Bemerkungen über die Endigung der Hautnerven u. den Bau der Muskeln. Zeitschr. f. wiss. Zool. 1857, Vol. VIII, p. 311.

*Krause, W.*, Ueber den Bau der quergestreiften Muskelfaser. Zeitschr. f. rat. Med. Vol. XXIII.

*Krause, W.*, Die Nervenendigungen in den Froschmuskeln. Internat. Monatschr. 1884. Vol. I, pp. 194–203.

*Krause, W.*, Die motorischen Endplatten, etc. Hannover, 1869.

*Krause, W.*, Ueber die Endigungen der Muskelnerven. Göttinger Nachrichten. 1863, p. 21.

*Krause, W.*, Ueber die Endigungen der Muskelnerven. Henle and Pfeufer’s Zeitschr. 1863. Vol. XX, pp. 1–19.

*Kühne, W.*, Untersuchungen über Bewegungen und Veränderungen der contractilen Substanzen. Arch. f. Anat. n. Phys. 1859, p. 816.

*Kühne, W.*, Die Muskelspindeln. Virchow’s Arch. 1864. Vol. XXVIII, pp. 528–538.

*Kühne, W.*, Untersuchungen über das Protoplasma und die Contractilität. Leipzig, 1864.

*Kühne, W.*, Ueber die peripherischen Endorgane der motorischen Nerven. Leipzig, 1862.

*Kühne, W.*, Zur Lehre von den Endplatten der Nervenhügel. Virchow’s Arch. 1866. Vol. XXXIV, pp. 412–422.

*Kühne, W.*, Ueber das Verhalten des Muskels zum Nerven. Verhandl. d. natur-hist.-med. Vereins zu Heidelberg. 1880. Vol. II, p. 227.

*Kühne, W.*, Ueber Nervenendigungen in den Muskeln nach Beobachtungen von M. B. van Sykel. Abdruk. aus den Verhandl. d. Naturh. med. Verein zu Heidelberg. 1884. Vol. III, pp. 238–242.

*Kühne, W.*, Wiederlegung der Bemerkung E. du Bois-Reymond’s über mehrfache. Nervenendigungen einer Muskelfaser. Zeitschr. f. Biol. 1884. Vol. XX, pp. 531–539.

*Kühne, W.*, Ueber die Endigung der Nerven in den Muskeln. Virchow’s Arch. 1866. Vol. XXVII, pp. 508–533.

*Kühne, W.*, and *Voit, C.*, Neue Untersuchungen über motorische Nervenendigung. Zeitschr. f. Biologie. Vol. XXXIII.

*Lavdowsky, M.*, Die feinere Struktur und die Nervenendigungen der Froschharnblase. Arch. f. Anat. u. Physiol. 1872, p. 55.

*Leboucq, H.*, Recherches sur le développement et la terminaison des nerves chez les larves des Batrachiens. Bull. de l’Acad. de roy. de Belgique. 1876. Vol. XLI, p. 561.

*Letzerich, L.*, Ueber die Endigungsweise der motorischen Nerven. Med. Centralz. 1863, No. 37.

*Leydig, F.*, Ueber Tastkörperchen und Muskelstructur. Arch. f. Anat. u. Physiol. 1856, p. 150.

*Löwit*, Die Nerven der glatten Muskulatur. Sitzungsb. d. Wiener Acad. 1875. Vol. LXXI, Pt. III, p. 355.

*Marshall, C. F.*, The structure and distribution of striped and unstriped muscle. Quart. Journ. Micros. Sci. 1887. Vol. XXV.

*Martin, H.*, Sur la structure de la fibre musculaire striée et sur les analogies de structure et fonction entre les tissus musculaires et les cellules à bâtonnets (protoplasma strié). Arch. de physiol. norm. et pathol. 1882, p. 465.

*Mayer, S.*, Die sogenannten Sarkoplasten. Anat. Anzeiger, 1886. No. 9, p. 231.

*Mayer, S.*, Einige Bemerkungen zur Lehre von der Rückbildung der quergestreiften Muskelfasern. Prager Zeitschr. f. Heilkde. 1887. Vol. VIII, p. 177.

*Mays, K.*, Histo-physiol. Untersuchungen über die Verbreitung der Nerven in den Muskeln. Zeitschr. f. Biol. Vol. XX.

*Mays, K.*, Ueber die Nervatur des Musculus rectus abdominis des Frosches. Heidelberg, 1886.

*Melland, B.*, A simplified view of the histology of the striped muscle-fibre. Quart. Journ. Micros. Sci. 1885. Vol. XXV, p. 371.

*Merkel, F.*, Der quergestreifte Muskel. Arch. f. mik. Anat. 1873. Vol. IX, pp. 293–367.

*Minra, M.*, Untersuchungen über die motorischen Nervenendigungen der quergestreiften Muskelfasern. Virchow’s Arch. 1886. Vol. CV, p. 129.

*Nasse, O.*, Zur Anatomie und Physiologie der quergestreiften Muskelfasern. Leipzig, 1882. Abstract in Centralbl. f. d. med. Wiss. 1882, pp. 884 and 908.

*Newman, D.*, New theory of contraction of striated muscle and demonstration of the composition of the broad dark bands. Journ. of Anat. and Physiol. 1879, p. 4.

*Nicolaides, R.*, Ueber die caryokynetischen Erscheinungen der Muskelkörper während des Wachstums der quergestreiften Muskeln. Arch. f. Anat. u. Physiol. 1883, p. 441.

*Odenias, M. W.*, Undersökungen öfer de sensibla muskelnervena. Nord. Medic. Arch. Vol. IV, No. 18.

*Paneth, J.*, Die Entwickelung von quergestreiften Muskelfasern aus Sarkoplasten. Wiener Sitzungsber. 1886. Vol. XCII, Pt. III, p. 561.

*Petrowsky*, Zur Frage über das Wachstum der Muskelfasern des Muskelgewebes beim Frosch. Med. Centralbl. No. 49, pp. 769–772.

*Pohl-Pincus*, Ueber die Muskelfasern des Froschherzens. Arch. f. mik. Anat. 1884, Vol. XXIII, p. 500; and Verhandl. der Physiol. Gesell. zu Berlin. 1882–3. No. 9.

*Ranvier, L.*, Appareils nerveux terminaux des muscles de la vie organique; cœurs sanguins, cœurs lymphatiques; œsophagus; muscles lisses. Leçons recueillies par Weber et Lataste. Leçons d’Anatomie générale faites au Collège de France. Paris, 1880. Vol. VII, p. 350.

*Ranvier, L.*, Leçons sur l’histologie du Système nerveux. 1878. Vol. II.

*Reichert, K. E.*, Ueber das Verhalten der Nervenfasern bei dem Verlauf und Endigung in einem Hautmuskel des Frosches, Rana temporaria. Arch. f. Anat. u. Physiol. 1851, p. 29.

*Retzius*, Zur Kenntniss der quergestreiften Muskelfaser. Biologische Untersuchungen. 1881, p. 1.

*Rouget*, Note sur la terminaison des nerfs moteurs dans les muscles chez les reptiles, les oiseaux et les mammifères. Comptes rendus. 1862. LV, p. 548.

*Sachs, C.*, Die quergestreifte Muskelfaser. Arch. f. Anat. u. Physiol. 1872, pp. 607–648.

*Sachs, C.*, Die Nerven der Sehnen. Arch. f. Anat. u. Physiol. 1875, p. 402.

*Sandmann, D. G.*, Ueber die Verteilung der motorischen Nervenendapparate in den quergestreiften Muskeln der Wirbelthiere. Arch. f. Anat. u. Physiol. 1885, p. 240.

*Schönn*, Anatomische Untersuchungen im Bereich des Muskel- und Nervengewebes. Jenaische Zeitschr. 1865. Vol. II, pp. 26–60.

*Schultze, M.*, Ueber Muskelkörperchen und das was man eine Zelle zu nennen habe. Arch. f. Anat. u. Physiol. 1816, p. 17.

*Sokolow, A. A.*, Sur les transformations der terminaisons des nerfs dans les muscles de la grenouille après les section des nerfs. Arch. de Physiol. normale et pathologique, 1874, pp. 300–315.

*Sokolow, A. A.*, Ueber die Nervenendigungen in den Muskeln ausgehungerter Frösche. Medicin. Bote. 1876, St. Petersburg.

*Tergast, P.*, Ueber das Verhältniss von Nerve und Muskel. Arch. f. mik. Anat. 1873. Vol. IX, p. 36.

*v. Thanhoffer, L.*, Beiträge zur Histologie und Nervenendigung der quergestreiften Muskelfasern. Arch. f. mik. Anat. 1882. Vol. XXI, p. 26.

*Thin, G.*, On the structure of muscular fibre. Quart. Journ. Microsc. Sci. 1877. Vol. XVI, pp. 251–259.

*Tolotschinoff*, Ueber das Verhalten der Nerven zu den glatten Muskelfasern der Froschharnblase. Arch. f. mik. Anat. 1869. Vol. V, p. 510.

*Trinchese, S.*, Mémoire sur la terminaison périphérique des nerfs moteurs dans la série animale. Journ. de l’Anat. et de la Physiol. 1867, pp. 485–504 (original in Italian, 1867).

*Tschiriew, S.*, Sur les terminaisons nerveuses dans les muscles striés. Arch. de physiol. norm. et path. 1879. Vol. VI, p. 89.

*Tschiriew, S.*, Sur les terminaisons nerveuses dans les muscles striés. Compt. rend. 1878. Vol. LXXXVII, p. 604.

*Unger*, Untersuchungen über die quergestreiften Muskelfasern des lebenden Thieres. Wiener med. Jahrb. 1879, p. 61; and in Centralbl. f. d. med. Wiss. 1879, No. 34, p. 622.

*Wagener, G. R.*, Ueber die Verbindung von Muskel und Sehne unter einander. Sitzungsber. naturw. Gesells. Marburg. 1874, pp. 38–46.

*Waldeyer, W.*, Ueber die Endigung der motorischen Nerven in den quergestreiften Muskeln. Centralbl. f. d. med. Wiss. 1863, p. 369.

*Waldeyer, W.*, Untersuchungen über den Ursprung und den Verlauf des Axencylinders bei Wirbellosen und Wirbelthieren, sowie über dessen Endverhalten in der quergestreiften Muskelfaser. Henle and Pfeuffer’s Zeitschr. 1864. Vol. XX, pp. 193–257.

*Weismann, A.*, Ueber die Musculatur des Herzens beim Menschen und in der Thierreihe. Arch. f. Anat. u. Physiol. 1861, p. 41.

*Wolff, W.*, Ueber den Zusammenhang des Muskels mit der Sehne. Diss. Berlin, 1877; Abstract in Centralbl. f. d. med. Wiss. 1877, p. 733.

Consult also: *Arnold, J., Kühne, W.*, and *Schweigger-Seidel, F.*, in Stricker’s Handbuch der Gewebelehre.

II. CARTILAGE AND BONE.

*Arnold, J.*, Ueber die Abscheidung des indigschwefelsauren Natrons im Knochengewebe. Virchow’s Arch. 1877. Vol. LXXI, p. 17.

*Arnold, J.*, Die Ausscheidung des indigschwefelsauren Narions im Knorpelgewebe. Virchow’s Arch. 1878. Vol. LXXIII, p. 125.

*Bigelow, W. S.*, Notiz über den Theilungsvorgang bei Knorpelzellen sowie über den Bau des Hyalinknorpels. Arch. f. mik. Anat. 1879. Vol. XVI, p. 457.

*Boll, F.*, Untersuchungen über den Bau und die Entwicklung der Gewebe. Arch. f. mik. Anat. 1871. Vol. VII, p. 275.

*Bruch, C.*, Ueber die Verknöcherung der Wirbelsäule bei den Batrachiern. Würzb. naturw. Zeitschr. 1862. Vol. III, pp. 225–238.

*Bush, F.*, Das Knochengewebe der Batrachier nach den Untersuchungen von N. Kastschenko. Verhandl. d. physiol. Gesells. zu Berlin. 1881, pp. 358–361.

*Flesch*, Untersuchungen über die Grundsubstance des Hyalinknorpels. Würzburg, 1880.

*Heidenhain*, Zur Kenntniss des hyalinen Knorpels. Studien aus d. physiol. Inst. zu Breslau. 1863. Pt. II, p. 1.

*Hertwig, O.*, Anatomisch histologische Untersuchung des Skelets der Mundhöhle und der Zähne der Amphibien; supplement to Vol. XI. Arch. f. mikroskopische Anat. 1874, pp. 29–32.

*Kastschenko, N.*, Ueber die Genese und Architectur der Batrachierknochen. Arch. f. mik. Anat. 1881. Vol. XIX, pp. 1–52.

*Kastschenko, N.*, Ueber die Krappfärbung der Froschgewebe. Arch. f. mik. Anat. 1882. Vol. XXI, p. 357.

*v. Kölliker*, Gewebelehre Leipzig. 1867, p. 66.

*Lehmann, J. C.*, Ueber den Knorpel in der Achillessehne des Frosches. Zeitschr. f. wiss. Zool. 1864. Vol. XIV, p. 109.

*Levschin, L.*, Ueber die Entwicklung des Knochengewebes des Frosches. Centralbl. f. med. Wiss. Nos. 18, 19.

*Mays, C.*, Ueber den Bau der Sehnen, etc. Virchow’s Arch. 1879. Vol. LXXV, p. 112.

*Renaud, M. J.*, Système hyalin de soutènement des centres nerveux et de quelques organes des sens. Arch. de Physiol. 1881, p. 6.

*Schleicher, W.*, Die Knorpelzelltheilung. Arch. f. mik. Anat. 1879. Vol. XVI, P. 248.

*Spina, A.*, Ueber die Saftbahnen des hyalinen Knorpels. Wiener Sitzungsber. 1879. Vol. LXXX, Pt. III, p. 267.

*Stadelmann, E.*, Die Histologie des ‘Pseudoknorpels’ in der Achillessehne des Frosches, etc. Virchow’s Arch. 1880, Vol. LXXX, p. 105; also as Dissert. inaug. Königsberg, 1878.

*van Stricht, O.*, Recherches sur le cartilage hyalin. Annales de la société de médicine de Grand. 1885, pp. 221–232.

*Thin, G.*, On the structure of hyaline cartilage. Quart. Journ. Micros. Sci. 1876. Vol. XVI, pp. 1–22.

*v. Török, A.*, Der feinere Bau des Knorpels des Achillessehne des Frosches. Centralbl. f. d. med. Wiss. 1872, No. 5, p. 66; and Verhandl. d. phys.-med. Gesells. zu Würzburg, 1872, Vol. III, pp. 1–26.

III. THE CONNECTIVE TISSUES.

*Billroth, T.*, Ueber die Epithelzellen der Froschzunge, den Bau des Cylinder- und Flimmerepithel und ihr Verhältniss zum Bindegewebe. Arch. f. Anat. u. Physiol. 1858, p. 159.

*Bizzozero, G.*, Ueber den Bau des Sehnengewebes. Moleschott’s Untersuchungen. 1876. Vol. XI, p. 36.

*Bobinzky, C.*, Zur Kenntniss des Baues, der Entwicklung and der regressiven Metamorphose der Fetzellen. Centralbl. f. d. med. Wiss. 1885. No. 43, pp. 753–755.

*Boll, F.*, Untersuchungen über den Bau und die Entwicklung der Gewebe. Arch. f. mik. Anat. 1871. Vol. VII, p. 276.

*Ciaccio, G. V.*, Nuove Ricerche sull’ interna tessitura dei tendi. Memorie dell’ Academie delle scienze dell Istituto di Bologna, 1872. Series III, Vol. II. Abstract in Centralbl. f. d. med. Wiss. 1873.

*Czumak, J.*, Notiz über elastische Sehnen. Centralbl. f. med. Wiss. 1863, p. 785.

*Flemming, W.*, Ueber Bildung und Rückbildung der Fettzelle im Bindegewebe; und Bemerkungen über die Structur des letztern. Arch. f. mik. Anat. 1871. Vol. VII, p. 32.

*Gerlach, J.*, Ueber Bindegewebe. Sitzungsb. d. phys.-med. Societät zu Erlangen. 1872, p. 78.

*Ginsburg, L.*, Ueber das Verhalten der Sehnenzellen bei der Entzündung. Virchow’s Arch. 1882. Vol. LXXXVIII, p. 263.

*Golgi, C.*, Sui Nervi dei Tendini dell’ Uomo e di altri Vertebrati e di un nuovo Organo nervoso terminale Musculo-tendineo. Estr. dalle Memorie della Reale Acc. di Torino. 1880. Series II, Vol. XXXII, p. 29; No. 6, p. 86.

*Hensen, V.*, Ueber die Entwicklung des Gewebes und der Nerven im Schwanze der Froschlarve. Virchow’s Arch. 1864. Vol. XXXI, p. 51.

*Hoyer*, Ueber den Bau der Cylinder- und Flimmerepithelien und ihr Verhältniss zum Bindegewebe. Arch. f. Anat. u. Physiol. 1858, p. 163; also Deutsche Klinik. 1857, No. 21.

*Iwanoff, A.*, Beiträge zur normalen und pathologischen Anatomie des Frosch-Glaskörpers. Centralbl. f. d. med. Wiss. 1868, p. 129.

*Kollmann*, Ueber den Bau der Sehne. Münchener Sitzungsber. 1878. Abstract in Centralbl. f. d. med. Wiss. 1879, p. 881.

*Maddox*, On the apparent relation of nerve to connective-tissue corpuscles. Proc. Roy. Soc. Lond. 1868. Vol. XVI, p. 61.

*Mays, C.*, Ueber den Bau der Sehnen mit besondere Berücksichtigung über Saftbahnen. Virchow’s Arch. 1879. Vol. LXXV, p. 112.

*Sachs, C.*, Die Nerven der Sehnen. Arch. f. Anat. u. Physiol. 1875, p. 402.

*Spina, A.*, Untersuchungen des lebenden Bindegewebes. Oesterr. med. Jahrb. 1884. Pt. II.

NOTE BY THE TRANSLATOR.

Reference has already been made to the views of Messrs. Melland and Marshall on the structure of muscle-fibres. The opinion that the striation of voluntary muscle is wholly or in part due to the presence of a regularly arranged network was previously published by Retzius, Bremer, and others. The authors referred to have now for the first time shown the importance of this network in all vertebrate muscular tissues, whether voluntary or involuntary.

Mr. Marshall gives the following summary of the result of his researches, which the Translator has confirmed by his own observations:--

1. In all muscles which have to perform rapid and frequent movements, a certain portion of the muscle is differentiated to perform the function of contraction, and this portion takes on the form of a very regular and highly modified intracellular network.

2. This network, by its regular arrangement, gives rise to certain optical effects which cause the peculiar appearances of striped muscle.

3. The contraction of the striped muscle-fibre is probably caused by the active contraction of the longitudinal fibrils of the intracellular network; the transverse networks appear to be passively elastic, and by their elastic rebound cause the muscle to rapidly resume its relaxed condition when the longitudinal fibrils have ceased to contract; they are possibly also paths for the nervous impulse.

4. In some cases where muscle has been hitherto described as striped, but gives no appearance of the network on treatment with the gold and other methods, the apparent striation is due to optical effects caused by a corrugated outline in the fibre.

5. In muscles which do not perform rapid movements, but whose contraction is comparatively slow and peristaltic in nature, this peculiar network is not developed. In most if not all of the unstriped muscles of invertebrates there does not appear to be an intracellular network present in any form, but in the unstriped muscle of vertebrates there are longitudinal fibres only; these possibly represent a form of network intermediate between the typical irregular intracellular network of other cells and the highly modified network of striped muscle.

6. The cardiac muscle-cells contain a network similar to that of ordinary striped muscle.

DESCRIPTION OF THE FIGURES ON PLATE II.

Fig. 180 (p. 278).

I. Preparation of the mucous membrane of the dorsal surface of the mouth and oesophagus to show the vascular supply. Arteries red, veins blue; after Schöbl.

II. Small portion of the above to show the dilatations on the capillaries; after Schöbl.

Fig. 187 (p. 285).

Transverse section through the mucous membrane of the fundus of the stomach of _Rana esculenta_. Alcohol preparation, doubly stained with carmine and anilin blue. After Biedermann. (Oc. II, Syst. 7, Hartnack.)

Fig. 196 (p. 298).

I. Partial injection of the liver from the portal vein (blue): _Rana esculenta_.--G. H.

II. Partial injection of the liver from the hepatic vein (red): _Rana esculenta_.--G. H.

III. Complete injection of the liver from the hepatic artery (red) and from the portal vein (blue): _Rana esculenta_.--G. H.

_A_ Portal (interlobular) veins and their branches. _B_ Hepatic (intralobular) veins and their branches. _C_ Hepatic arteries and their branches.

Fig. 208 (p. 318).

Two sections from the lung of _Rana temporaria_; stained with borax-carmine.--G. H.

I. The lung dilated (Hartnack, Oc. I, Syst. 3).

II. The lung contracted (Hartnack, Oc. I, Syst. 7).

_A_ Band of muscle cut transversely. _B_ Band of muscle cut longitudinally. _C_ Muscular layer of surface.

Fig. 217 (p. 334).

Portions of two transverse vertical sections through the kidney.--G. H.

I. Kidney of _Rana esculenta_, partial injection of the uriniferous tubes with silver nitrate (Hartnack, Oc. I. Syst. 7).

II. Kidney of _Rana temporaria_, stained with borax-carmine (Hartnack, Oc. I, Syst. 7).

Fig. 219 (p. 337).

Two portions from a gold preparation of the kidney of _Rana esculenta_.--G. H.

I. Showing the tendency to split into lobules.

II. Nerve-fibres accompanying the blood vessels.

_a_ Blood-vessels. _b_ Nerves.

APPENDIX.

I. WORKS WHICH DESCRIBE ORGANS OR SETS OF ORGANS IN THE FROG.

*Bettade, E.*, Sulle diverse forme delle R. temp. in Europa e più particolammente nell’ Italia. Venezia, 1885.

*Brehm, A. C.*, Illustriertes Thierleben. Hildburghausen, 1869. Vol. V.

*Burdon-Sanderson*, Handbook for the Physiological Laboratory. London, 1873.

*Camerana, L.*, Recherches sur les variations de in R. esculenta et du Bufo viridis dans le bassin de la Méditerranée. Paris, 1883.

*Carus, C. G.*, Lehrbuch der vergleichenden Zootomie. 2nd Edit. Leipzig, 1834.

*Cepède, Comte de la*, Histoire naturelle des quadrupèdes ovipaires et des serpens. Paris, 1808.

*Dugès*, Recherches anatomiques et physiologiques sur les Reptiles. Ext. des Annales des Sciences naturelles. Paris, 1827.

*Duméril and Bibron*, Erpétologie générale ou histoire complète des Reptiles. 1836.

*Ecker, A.*, Icones physiologicae. Leipzig, 1851–1859.

*Fatio, V.*, Faune des vertébrés de la Suisse. Genève et Bâle, 1872.

*Gegenbaur, C.*, Grundzüge der vergl. Anatomie. Leipzig, 1870.

*Gegenbaur, C.*, Grundriss der vergl. Anatomie. Leipzig, 1878.

*Gerlach*, Handbuch der Histologie. 1853–1854.

*Gesner, C.*, Historia Animalium. Liber I. 1551.

*Gesner, C.*, Icones Animalium. 1560.

*v. Griesheim, A.*, Ueber die Zahlenverhältnisse der Geschlechter bei R. fusca. Pflüger’s Arch. f. d. ges. Physiol. 1881. Vol. XXVI, p. 3.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Vol. VI, Amphibien. Leipzig, 1873–1878.

*Howes, G. B.*, An Atlas of Practical Elementary Biology. London, 1885.

*Huxley, T.*, Anatomy of the Vertebrated Animals. London, 1871.

*Huxley, T.*, Lectures on the Elements of Comparative Anatomy.

*Huxley, T.*, Article Amphibia, Encyclopaedia Britannica. IXth Edit. 1875.

*Klein, E.*, Beiträge zur Anatomie der ungeschwänzten Batrachier. Jahreshefte. Württemberg, 1850, pp. 1–84.

*Klein, E.*, and *Noble Smith*, Atlas of Histology. London, 1879–1880.

*Kloezke, C. G.*, Dissertatio anatomica de Rana cornuta. Berolini, 1816.

*v. Kölliker, A.*, Handbuch der Gewebelehre. 5th Edit. Leipzig, 1867.

*Kuhl, H.*, Beiträge zur Zoologie der Rana esculenta: in Beitr. z. Zool. Frankfurt a. M., 1820.

*Laurenti, J. N.*, Synopsis Reptilium. Viennae, 1768.

*Leydig, F.*, Lehrbuch der Histologie. Frankfurt a. M., 1857.

*Marshall, A. M.*, The Frog. 3rd Edit. London and Manchester, 1888.

*Mayer, A. F.*, Beiträge zu einer anatomischen Monographie der Rana pipa. Acad. Caes. Leop. Nov. Acta, 1825. Vol. XII, p. 527.

*Meckel, J.*, Beiträge zur vergleichenden Anatomie. Leipzig, 1811.

*Meckel, J.*, System der vergleichenden Anatomie. Halle, 1833.

*Mivart, St. Geo.*, On the Classification of the Anurous Batrachians. Proc. Zool. Soc. 1869.

*Mivart, St. Geo.*, The Common Frog. London, 1874.

*Müller, J.*, Beiträge zur Anatomie und Naturgeschichte der Amphibien. Tiedemann’s Zeitschr. 1831, p. 190.

*Müller, J.*, The Physiology of the Senses, etc. Translated by W. Baly. London, 1848.

*Owen, R.*, Anatomy of the Vertebrates. London, 1866.

*Ranvier, L.*, Leçons d’anatomie générale. Paris, 1880.

*Rösel v. Rosenhof*, Historia naturalis ranarum nostratium. Nürnberg, 1758.

*Rudolphi and Breyer*, Observationes anatomicae circa abricam Ranae pipae. Berolini, 1811.

*Rusconi, M.*, Développement de la grenouille commune. Milan, 1826.

*Schneider, J. G.*, Historia amphibiorum. Jenae, 1799.

*Schwalbe, G.*, Lehrbuch der Anatomie der Sinnesorgane. Erlangen, 1885.

*Stannius, H.*, Zootomie der Amphibien (Handb. der Zoot. der Wirbelthiere, 2 Buch). 2nd Edit. Berlin, 1856.

*Stricker, S.*, Beiträge zur Biologie der Batrachier. Wien. Zool. Bot. Verhandl. 1866. Vol. XVI, pp. 451–456.

*Stricker, S.*, Handbuch der Gewebelehre.

*Stricker, S.*, Manual of Human and Comparative Histology. Translated by H. Power. London, 1870.

*Swammerdam, J.*, Biblia Naturae Amstelodamensis. (Dutch and Latin by Gaubius. Leidae, 1738.)

*Todd and Bowman*, The Physiological Anatomy and Physiology of Man. London, 1845–1857.

*Vogt, C.*, Zoologische Briefe. Frankfurt a. M., 1851.

*Wagler, J.*, Natürliches System der Amphibien. München, Stuttgart, and Tübingen, 1830.

*Wagner, R.*, Lehrbuch der vergleichenden Anatomie. Leipzig, 1834–1835.

*Wagner, R.*, Icones Zootomicae. Leipzig, 1841.

*Wagner, R.*, Handwörterbuch der Physiologie. 1842.

*Waters, W. H.*, Histological Notes. Manchester and London, 1884.

*Wiedersheim, R.*, Lehrbuch der vergleichenden Anatomie der Wirbelthiere. 2nd Edit. Jena, 1886.

*Wiedersheim, R.*, Elements of Comparative Anatomy of Vertebrates. Translated by N. Newton Parker. London, 1886.

II. WORKS RELATING TO THE EMBRYOLOGY AND DEVELOPMENT OF THE FROG.

*Balfour, F. M.*, Treatise on Comparative Embryology. London, 1880.

*Born, G.*, Beiträge zur Bastardirung zwischen den einheimischen Anurenarten. Pflüger’s Arch. f. d. ges. Physiol. 1883. Vol. XXXII, p. 453.

*Durham, H. E.*, Note on the presence of a Neurenteric Canal in Rana. Quart. Journ. Micros. Sci. 1886. Vol. XXVI, p. 509.

*Giles, A. E.*, The development of the fat-bodies in Rana temporaria. Quart. Journ. Micros. Sci. 1888. Vol. XXIX.

*Goette, A.*, Kurze Mittheilungen aus der Entwicklungsgeschichte der Unke. Arch. f. mik. Anat. 1873. Vol. IX, p. 396.

*Goette, A.*, Entwicklungsgeschichte der Unke. Leipzig, 1875.

*Hertwig, O.*, Die Entwicklung des mittleren Keimblattes der Wirbelthiere. Jena, 1883.

*Johnson, A.*, and *Sheldon, L.*, Notes on the Development of the Newt (Triton cristatus). Quart. Journ. Micros. Sci. 1886. Vol. XXVI, p. 573.

*Marshall, A. M.*, The Frog: An Introduction to Anatomy, Histology, and Embryology. 3rd Edition. Manchester and London, 1888.

*Pflüger, E.*, Einige Beobachtungen zur Frage über die das Geschlecht bestimmenden Ursachen. Pflüger’s Arch. f. d. ges. Physiol. 1881. Vol. XXVI.

*Pflüger, E.*, Hat die Concentration des Samens einen Einfluss auf das Geschlecht? Pflüger’s Arch. f. d. ges. Physiol. 1883. Vol. XXIX, p. 1.

*Pflüger, E.*, Zusammenstellung der Ergebnisse und Erörterung der Principien der Zeugung. Pflüger’s Arch. f. d. ges. Physiol. 1883. Vol. XXXII, p. 542.

*Pflüger, E.*, and *Smith, W. J.*, Experimente über Bastardirung der anuren Batrachier. Pflüger’s Arch. f. d. ges. Physiol. 1883. Vol. XXXII, p. 519.

*Remak*, Untersuchungen über die Entwickelung der Wirbelthiere. Berlin, 1855.

*Schultze, O.*, Zur ersten Entwickelung des braunen Grasfrosches. Leipzig, 1887.

*Schultze, O.*, Die Entwicklung der Keimblätter und der Chorda dorsalis von Rana fusca. Zeitschr. f. wiss. Zool. 1888. Vol. XLVII, p. 325.

*Spencer, W. B.*, Some Notes on the Early Development of Rana temporaria. Quart. Journ. Micros. Sci. 1885. (Supplement.)

*Stricker, S.*, Untersuchungen über die Entwicklung des Kopfes der Batrachier. Arch. f. Anat. u. Physiol. 1864, p. 52.

*Törok, A.*, Beiträge zur Kenntniss der ersten Anlagen der Sinnesorgane und der primären Schädelformation bei den Batrachiern. Moleschott’s Untersuchungen, 1870. Vol. X, p. 338.

III. ADDITIONS TO THE LISTS GIVEN AT THE HEADS OF THE SECTIONS.

1. THE BONES.

*Albrecht, P.*, Note sur le basi-occipital des batraciens anoures. Extr. d. Bullet. d. Musée royal d’hist. nat. de Belgique. 1883. Vol. II.

*Born, G.*, Die sechste Zehe der Anuren. Morphol. Jahrb. 1876. Vol. I.

*Born, G.*, Ueber das Skelet des Fersenhöckers von Rana fusca, etc. Sitzungsb. d. Schles. Gesell. f. vaterländ. Cultur. 1879.

*Born, G.*, Nachträge zu Carpus und Tarsus. Morph. Jahrb. 1880. Vol. VI.

*Ecker, A.*, Icones physiologicae. Leipzig, 1881–1889.

*Ecker, A.*, Die Anatomie des Frosches. 2nd Edition. Braunschweig, 1888, pp. 17–62.

*Gegenbaur*, Untersuchungen zur vergl. Anatomie der Wirbelsäule bei Reptilien und Amphibien. Leipzig, 1862.

*Gegenbaur*, Grundzüge der vergl. Anatomie. Leipzig, 1870.

*Goette, A.*, Brustbein und Schultergürtel auf entwickelungsgeschichtlicher Grundlage verglichen bei Amphibien und Anurioten. Arch. f. mik. Anat. 1877. Vol. XIV, p. 502.

*Howes, G. B.*, On some abnormalities of the Frog’s vertebral column. Anat. Anz. 1886. Vol. I, Pt. II.

*Leydig, F.*, Ueber den Bau der Zehen bei Batrachiern und die Bedeutung des Fersenhöckers. Morphol. Jahrb. 1876. Vol. II.

*Parker, W. K.*, A monograph on the structure and development of the shoulder-girdle and sternum. Ray. Soc. 1867.

*Schneider, J. G.*, Historia amphibiorum. Jenae, 1799.

*Stöhr, P.*, Zur Entwickelungsgeschichte des Anurenschädels. Zeitschr. f. wiss. Zool. 1881. Vol. XXXVI.

*Törok, A.*, Beiträge zur Kenntniss der ersten Anlagen der Sinnesorgane und der primären Schädelformation bei den Batrachiern. Moleschott’s Untersuchungen. 1870. Vol. X, p. 338.

2. THE MUSCLES.

*Albrecht, P.*, Beitrag zur Morphologie des M. omohyoides und der ventralen inneren Interbranchial-Musculatur. Inaug. Dissert. Kiel, 1876.

*Ecker, A.*, Die Anatomie des Frosches. 2nd Edition. Braunschweig, 1888, pp. 65–139.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Vol. VI. Amphibien. Leipzig, 1873–1878.

*Howes, G. B.*, An Atlas of Practical Elementary Biology. London, 1885.

3. NERVOUS SYSTEM.

*Engelmann, T. W.*, Ueber die Discontinuität des Axencylinders und den fibrillären Bau der Nervenfasern. Pflüger’s Arch. f. d. ges. Physiol. 1880. Vol. XXII, p. 1.

*Grandry*, Recherches sur la structure interne du cylindre de l’axe et des cellules nerveuses. Bull. de l’Acad. Roy. du Belgique. 1868.

*Hodge, C. F.*, Some effects of stimulating ganglion-cells. (Some anatomical details regarding the relations of nerve-fibres with nerve-cells are given.) American Journ. of Phys. 1888.

*Owsjannikow, P.*, Ueber die Rinde des Grosshirns. Mémoires de l’acad. impériale des sciences de St. Pétersbourg. 1879. Series VII, Vol. XXVI, No. 11.

*Spiro*, Physiologisch-topographische Untersuchungen am Rückenmark des Frosches. Mémoires de l’acad. impériale des sciences de St. Pétersbourg. 1870. Series VII, Vol. XVI, No. 7.

*Waldeyer, W.*, Untersuchungen über den Ursprung und Verlauf des Axencylinders. Henle u. Pfeuffer’s Zeitschr. 1864. Vol. XX, pp. 193–257.

Consult also: *Gerlach, J.*, *Mayer, S.*, and *Schultze, M.*, in Stricker’s Handbuch der Gewebelehre.

4. THE VASCULAR SYSTEM.

*Barthol, P.*, Sopra il sistema linfatico dei Rettili. Pavia, 1833.

*Blaschek, A.*, Untersuchungen über Herz, Pericard, Endocard, und Pericardhöhle. Schenk’s Mitt. 1885. New Series, p. 32.

*Eberth, C. J.*, in Stricker’s Handbuch der Gewebelehre.

*Klein, E.*, On the peripheral distribution of non-medullated nerve-fibres (nerves of the blood-vessels in the frog’s tongue). Quart. Journ. Micros. Sci. 1872. Vol. XII, p. 123.

*Mayer, S.*, Studien zur Histologie und Physiologie des Blutgefässsystems. Wiener Sitzungsb. 1886. Vol. XCIII, Pt. III, p. 45.

*v. Recklinghausen, F.*, (The lymphatics) in Stricker’s Handbuch der Gewebelehre.

*Rollett, A.*, (The Blood) in Stricker’s Handbuch der Gewebelehre.

*Teichmann, L.*, Untersuchungen über das Saugadersystem. Leipzig, 1861.

5. THE ALIMENTARY CANAL.

*Heidenhain, R.*, Beiträge zur Kenntniss des Pancreas. Pflüger’s Arch. f. d. ges. Physiol. 1875. Vol. X, p. 557.

*Krause, W.*, Anatomische Untersuchungen (Tongue). Hannover, 1861.

Consult also: *Klein, E.*, The Oral Cavity and the Oesophagus; *Müller, W.*, The Spleen; *Eberth, C. J.*, The Liver, in Stricker’s Handbuch der Gewebelehre.

6. THE LUNGS AND LARYNX.

*Holmgren, F.*, Methode zur Beobachtung des Kreislaufs in der Froschlunge. Beitr. z. Anat. u. Physiol. Festgabe f. C. Ludwig. Leipzig, 1874.

*Meckel, J. F.*, Beiträge zur Geschichte des Respirations-Systemes der Amphibien. Meckel’s Arch. 1849. Vol. V.

*Schmidt, C.*, De l’épithelium pulmonaire. 1866.

*Williams*, Article Respiration, in Todd’s Cyclopaedia of Anat. and Physiol. 1859. Vol. V.

7. THE URINO-GENITAL SYSTEM, THE ADRENALS, AND THE FAT-BODIES.

*Aeby, C.*, Ueber glatte Muskelfasern im Ovarium und Mesovarium von Wirbelthieren. Arch. f. Anat. u. Physiol. 1859, p. 675.

*Giles, A. E.*, The development of the fat-bodies in Rana temporaria. Quart. Journ. Micros. Sci. 1888. Vol. XXIX.

*Grohe, F.*, Ueber die Bewegung der Samenkörper. Virchow’s Arch. 1865. Vol. XXXII, p. 416.

*Virchow, R.*, Ueber die Dotterplättchen bei den Fischen und Amphibien. Zeitschr. f. wiss. Zool. 1849. Vol. IV.

Consult also: *Eberth, C. J.*; *v. La Valette St. George*; *Ludwig, C.*; *Grünwald*; *Obersteiner, H.*; and *Stricker, S.*, in Stricker’s Handbuch der Gewebelehre.

8. THE SKIN AND SENSE-ORGANS.

a. _The Skin._

*Busch, A.*, Phänomene aus dem Leben der Pigmentzellen. Arch. f. Anat. u. Physiol. 1856, p. 415.

b. _Special Organs of Tactile Sensation._

*Mitrophanow, P.*, Zur Entwicklungsgeschichte und Innervation der Nervenhügel der Urodelenlarven. Biologisches Centralb. 1887, p. 174.

c. _The Organs of Taste._

*Beale, L. S.*, New Observations upon the Minute Anatomy of the Papillae of the Frog’s Tongue. Phil. Trans. 1865. Vol. CLV, p. 443.

*Engelmann, T. W.*, in Stricker’s Handbuch der Gewebelehre.

*Maddox, R. L.*, A Contribution to the Minute Anatomy of the Fungiform Papillae and terminal arrangement of Nerve to striped Muscular Tissue in the Tongue of the common Frog. Monthly Micros. Journ. 1869, p. 1.

d. _The Ear._

*Albrecht, P.*, Sur la valeur morphologique de la trompe d’Eustache. Communication faite à la Société d’Anatomie Pathologique de Bruxelles. 1884.

*v. Kölliker*, Handbuch der Gewebelehre. 5th Edit. Leipzig, 1867.

*Leydig, F.*, Handbuch der Histologie. Frankfurt a. M., 1857.

*Rüdinger*, in Stricker’s Handbuch der Gewebelehre.

e. _The Nose._

*Marshall, A. M.*, Morphology of the Vertebrate Olfactory Organ. Quart. Journ. Micros. Sci. 1879. Vol. XIX, p. 330.

f. _The Eye._

*Ciaccio, G. V.*, Beobachtungen über den inneren Bau des Glaskörpers im Auge des Menschen und der Wirbelthiere im Allgemeinen. Moleschott’s Untersuchungen, 1870. Vol. X, p. 383.

*Hannover* and *Finkbeiner*, Vergleichende Untersuchungen der Stärke des Glaskörpers bei den Wirbelthieren. Zeitschr. f. wiss. Zool. 1855. Vol. VI, p. 335.

*Hirschberg, J.*, Zur Dioptric und Ophthalmologie der Fish- und Amphibienaugen. Arch. f. Anat. u. Physiol. 1887, p. 493.

*Ranvier, L.*, Le mécanisme de la Sécrétion. Leçons faites au Collége de France en 1886–1887. (Nictitating membrane.)

Consult also: *Rollett* and *Stieda*, in Stricker’s Handbuch der Gewebelehre.

INDEX.

Abducens nerve, p. 171.     "    nucleus, 146. Acetabulum, 48. Acromial, 39. Adrenals, 348. Ala magna, 25.  "  temporalis, 25. Alar cartilages, 28. Alimentary canal, 258. Ampulla anterior, 396.    "    external, 398.    "    posterior, 398. Angulo-splenial, 34. Ankle, 50. Anterior ampulla, 396.    "     brachial lymph-sac, 259.    "     brachio-radial septum, 258.    "     brachio-ulnar septum, 258.    "     chamber, 409. Aorta dorsal, 233. Aponeurosis plantaris, 105. Arachnoid, 162. Arteria basillaris, 163.    "    bulbi, 222.    "    circumflexa genu. lat. sup., 238.    "          "       "    "   inf., 238.    "          "       "   med. sup., 238.    "          "       "    "   inf., 238.    "    comm. ant., 163.    "    coraco-clavicularis, 231.    "    costo-cervicalis, 231.    "    cruris inf., 239.    "    cut. calcanei, 239.    "    cut. fem. med., 237.    "     "    "   post., 237.    "     "   pectoris, 231.    "    haemorrhoid. inf., 236.    "    lobi hemisph. inf. ext., 163.    "      "     "     sup. int., 163.    "      "  optici, 163.    "    malleol. lat., 240,    "    malleol. med., 240.    "    pharyngo-maxill., 230.    "    ramus auricularis, 228, 230.    "      "   maxillaris comm., 228.    "      "       "      inf., 230.    "      "       "      sup., 228.    "      "   orbito-nasalis, 228.    "    scapularis post., 232.    "        "      sup., 232.    "    spinalis ant., 163.    "    subscapularis, 232.    "    suralis, 239. Arteries, 222.    "   of brain, 162.    "   of choroid, 411.    "   of foot, 240.    "   of hyaloid, 421.    "   of iris, 413.    "   of skin, 376.    "   of vitreous body, 421. Artery, ant. palatine, 224.    "     "   tibial, 239.    "   brachial, 232.    "   carotid, 224.    "   ciliary, 226.    "   coeliaco-mesenteric, 233.    "   femoral, 236.    "   gastric, 233.    "   haemorrhoidal, 235.    "   hepatic, 298.    "   hyaloid, 226.    "   iliac, 235.    "   internal carotid, 225.    "   laryngeal, 226.    "   lingual, 224.    "   lumbar, 235.    "   mesenteric, 234.    "   occipital, 228.    "   occipito-vertebral, 226.    "   oesophageal, 226.    "   ophthalmic, 225, 411, 413.    "   peroneal, 231.    "   pharyngeal, 224.    "   post. palatine, 224.    "   radial, 232.    "   renal, 333.    "   sciatic, 236.    "   spermatic, 236.    "   subclavian, 231.    "   tibial, 238.    "   ulnar, 233.    "   urino-genital, 235.    "   vertebral, 226.    "   vesico-epigastric, 235. Articular processes, 17. Articulations of vertebrae, 19.       "       of atlas, 24. Arytenoid cartilages, 313. Astragalus, 50. Atlas, 18. Auditory nerve, 172. Auditory nucleus, 144. Auerbach’s plexus, 292. Auricles, 214. Auriculo-ventricular valves, 216. Axillary septum, 258. Axis-cylinder, 202.

Bidder’s ganglion, 220. Bile-ducts, 298. Bladder, gall-, 295, 299.    "     urinary, 338. Blood, 262. Bones and joints, 13. Bowman’s glands, 387. Brachial nerve, 183. Brachio-ulnar lymph-sac, 259.    "    radial   "     , 259. Brain, 141.

Calcaneum, 50. Calcified cartilage, 15. Canales coccygei, 21. Canalis vertebralis, 20.    "    rami ant. acustici, 393. Capitulum radii, 43. Capsule of labyrinth, 391.    "    of lens, 413. Carotid arch, 222.    "    gland, 223. Cartilage, calcified, 15.     "      of shoulder-girdle, 40.     "      of skull, 29. Cartilages of larynx, 312.     "      of nose, 27, 385. Cauda equina, 135, 189. Cava recto-vesicalis, 304. Cavitas sigmoidea maj., 43. Central canal of cord, 137.    "    group of cells, 139. Cerebellum, 148. Cerebral hemispheres, 156. Chamber, anterior, 409.    "     posterior, 420. Chiasma, optic, 153, 155, 167. Chorda dorsalis, 20. Chordae tendineae, 216. Choroid coat, 409.    "    plexus of fourth vent., 142, 164.    "       "      third   "   , 153, 164. Ciliary nerves, 169.    "    processes, 420. Circulus iridis major, 413. Clavicle, 39. Cloaca, 347. Columella auris, 25, 390. Commissura anterior, 159.     "      inferior, 140.     "      posterior, 159.     "      superior, 140.     "      transversa, 154. Common bile-duct, 296. Cones, 418. Conus medullaris, 135. Coracoid, 39. Coracoid foramen, 39. Cornea, 406. Corpora quadrigemina, 152. Corpus callosum, 158, 159.    "   striatum, 158, 159. Corpuscles of blood, 263.     "      of Hassall, 321. Coverings of brain and cord, 162. Cranial nerves, 141, 167. Cranium, 23. Cricoid cartilage, 312. Crista acustica, 397.    "   deltoidea, 41.    "   medialis, 42. Crusta, petrosa, 279. Cupula terminalis, 398. Cutaneous glands, 372. Cuticula dentis, 279. Cutis, 369. Cystic duct, 295.

Dentale, 35. Dentary, 34. Dentine, 279. Descemet’s membrane, 407. Dorsal lymph-sac, 255.    "   roots, 140.    "   septum, 252. Duct, common bile-, 296.   "   cystic, 295. Ductus choledocus, 296.    "   endolymphaticus, 398.    "   fenestra ovalis, 394.    "   perilymphaticus, 395.    "   Wirsungianus, 301. Dura mater, 162.

Ear, 389. Enamel, 279. Enlargements of cord, 133, 137. Epicoracoids, 37. Epidermis, 367. Epiglottis, 317. Episternum, 36. Epithelium of ventricles, etc., 160. Exoccipitals, 23. External limiting membrane, 420. Extrastapedial, 26, 390. Eye, 405. Eyelids, 422.

Facial nerve, 171. Fat-bodies, 348. Femoral lymph-sac, 260. Fibrae arcuatae cerebelli, 149. Fibres of brain, 161. Filiform papillae, 380. Filum terminale, 135. Foramen condyloideum, 24.    "    magnum, 23.    "    Monroi, 157.    "    ovale, 24.    "    parietale, 156.    "    rotundum, 392. Formatio reticularis, 140. Fossa condyloidea, 24.   "   tympanica, 24. Fourth ventricle, 142. Fronto-parietal bones, 26. Fungiform papillae, 380.

Gall-bladder, 295, 299. Ganglia of bladder, 340.    "    of heart, 220.    "    of spinal, 177. Ganglion ciliare, 168.    "     condyloideum, 173.    "     Gasserii, 168.    "     interpedunculare, 152.    "     layer, 415.    "     nervi vagi, 173. Gasserian ganglion, 168. Glands, Bowman’s, 387.    "    cutaneous, 372.    "    gastric, 285.    "    Harder’s, 424.    "    intermaxillary, 280.    "    Lieberkühn’s, 288.    "    nasal, 386.    "    oesophageal, 283.    "    of nictitating membrane, 423.    "    periganglionic, 180.    "    thymus, 320.    "    thyroid, 322. Glossopharyngeal nerve, 172. Goblet-cells, 289. Goll’s columns, 140. Grey matter, 139.

Hair-cells of ear, 404.     "      of nose, 388. Harder’s glands, 424. Hassall’s corpuscles, 321. Heart, 213, 214.   "   endothelium, 320.   "   muscle, 216.   "   nerves, 219.   "   structure of, 216. Hepatic arteries, 421.    "    portal system, 248.    "    veins, 297. Hip-joint, 49. Humerus, 41. Hyaloid artery, 421.    "    membrane, 421. Hyoid, 35. Hypoglossal nerve, 182.

Ilia, 47. Iliac lymph-sac, 257.   "   septum, 253. Inferior femoral septum, 259.     "    sinus, 383. Infundibulum, 153. Inguinal septum, 254. Inner molecular layer, 415.   "   nuclear     "  , 416. Interfemoral lymph-sac, 260. Intermaxillary glands, 280. Intermediate fem. septum, 259. Internal ear, 391.     "    limiting membrane, 414, 420.     "    muscles of eye, 413. Interstapedial, 25, 391. Intestine, 286. Intumescentia ant. and post., 135. Iris, 412. Ischia, 48.

Kidney, 332. Knee-joint, 50.

Labyrinth membranous, 395.     "     osseous, 391.     "     structure, 402. Lachrymal duct, 387. Lagena cochlea, 400. Lamina fusca, 411.    "   suprachoroidea, 411.    "   terminalis, 153, 157. Large intestine, 292. Laryngeal nerve, 175. Larynx, 311. Lateral group of cells, 139.    "    lymph-sac, 255.    "    sense-organs, 379.    "    sinus, 380. Lens, 413. Lieberkühn’s glands, 288, 293. Ligament. calcanei, 19.     "     coronarium, 303.     "     gastro-duodenale, 305.     "     hepato-duodenale, 287, 295, 305.     "     intercruralia, 19.     "     interspinalia, 19.     "     pectinatum iridis, 409.     "     suspensor. hepatis, 304.     "     verteb. comm. ant., 19.     "        "      "   post., 19. Limiting membrane, external, 420.     "       "      internal, 414, 420. Lips, 275. Literature on adrenals, 330.      "     "  alimentary canal, 268.      "     "  blood, 211.      "     "  blood-vessels, 205.      "     "  bones and joints, 13.      "     "  cartilage, 431.      "     "  connective tissues, 432.      "     "  ear, 356.      "     "  embryology, 436–437.      "     "  eye, 360.      "     "  fat-bodies, 330.      "     "  gall-bladder, 272.      "     "  general, 435–436.      "     "  heart, 205.      "     "  intestine, 270.      "     "  larynx, 309.      "     "  liver, 272.      "     "  lungs, 309.      "     "  lymph, 211.      "     "  lymphatic system, 209.      "     "  mouth, 268.      "     "  muscle structure, 427.      "     "  muscles, 54.      "     "  nervous system, 122.      "     "  nose, 357.      "     "  pancreas, 272.      "     "  peritoneum, 274.      "     "  respiratory system, 309.      "     "  skin, 353.      "     "  spleen, 273.      "     "  taste-organs, 356.      "     "  thymus, 310.      "     "  thyroid, 310.      "     "  touch-organs, 356.      "     "  urino-genital system, 326. Liver, 294.   "   cells, 298.   "   pigment of, 299.   "   vessels of, 297. Lower eyelid, 422.   "   nasal glands, 386. Lungs, 317. Lymph, 264. Lymph-hearts, 261, 264. Lymph-sacs of ant. extremity, 258.   "    "   of hinder extremity, 259.   "    "   of trunk, 251, 255, 264. Lymphatic system, 251.

Macula lutea, 419. Malpighian bodies of kidney, 334.      "        "   of spleen, 303. Mandible, 34. Maxillary bones, 32.     "     septum, 253. Meckel’s cartilage, 35. Mediostapedial, 25, 390. Medulla oblongata, 142. Medullary segments, 202.     "     sheath, 201. Medullated nerves, 201. Meissner’s plexus, 291. Membrana choriocapillaris, 411.     "    limitans ext., 420.     "        "    int., 414, 420.     "    nictitans, 58, 422.     "    suprachoroidea, 411. Membrane of Descemet, 407. Membranous labyrinth, 395. Mentomeckelian cartilage, 35. Mesocephalic ganglion, 168. Metacarpus, 46. Metatarsus, 52. Meynert’s fibres, 155. Molecular layer, inner, 415.     "       "    outer, 419. Motor-oculi, 167. Mouth, 275. Movements of hand, 46. Mucous glands of skin, 375. Müller’s fibres, 420. Muscle, histology, 433. Muscles, 53. Muscles of abdomen, 67.    "    "  back, 71.    "    "  cloaca, 347.    "    "  eye, external, 55.    "    "  " internal, 413.    "    "  face, 59.    "    "  foot, 105.    "    "  forearm, 84.    "    "  forelimb, 75.    "    "  hand, 87.    "    "  hinder limb, 94.    "    "  hyoid, 64.    "    "  larynx, 315.    "    "  lower jaw, 60.    "    "  skin, 119. Musc. abduct. dig. I brev., 114.   "     "      "   II "   , 92.   "     "      "   " long., 91.   "     "      "   V, 113.   "     "      "   V brev., 116.   "     "      "   I long., 110.   "     "      "   II " , 86.   "     "      "   V prim., 91.   "     "      "   V secund., 91.   "     "     hallucis, 109.   "     "     pollicis, 87.   "     "     brev., 114.   "   adduct. brev., 100.   "     "     dig. I long., 109.   "     "      "   II, 89.   "     " " V, 113.   "     " longus, 99.   "     " magnus, 99.   "     " pollicis, 87.   "   anconaei, 87.   "   antibrachii lat., 85.   "        "      med., 85.   "        "      prof., 85.   "   biceps fem., 96.   "   coccygeo-cutaneus, 120.   "      "    -iliacus, 74.   "   coccygeo-sacralis, 73.   "   compressor cloacae, 348.   "   constrictor aditus laryngis, 315.   "   constrictor iridis, 413.   "   coraco-humeralis, 82.   "   cucullaris, 71.   "   cutaneus dorsi, 119.   "       "    pectoris, 119.   "   dilator aditus laryngis, 315.   "   deltoideus, 82.   "   depressor maxill. inf., 60.   "       "     palpebrae inf., 58.   "   dilator iridis, 413.   "      "    narium, 59.   "   extensor brevis, 106.   "      "     carpi ulnaris, 86.   "      "     cruris brevis, 104.   "      "     digit. I   brev., 114.   "      "       "    "   long., 114.   "      "       "    II  brev., 114.   "      "       "    "   long., 114.   "      "       "    "   prop. brev., 92.   "      "       "    "    "    long., 92.   "      "       "    III brev., 115.   "      "       "    "   long., 115.   "      "       "    "   prop., 93.   "      "       "    IV, 116.   "      "       "    "   brev., 116.   "      "       "    "   prop., 93.   "      "       "    V   brev., 115.   "      "       "    "   long., 115.   "      "       "    "   comm. brev., 91.   "      "       "    "     "   long., 87.   "      "     dorsi com  m., 73.   "    flex. antibrach. lat. superf., 85.   "      "       "      med., 85.   "      "       "      prof., 85.   "      "   brev. digit. I, 100.   "      "     "     "    IV, 112.   "      "     "     "    V, 113.   "      "   carpi radialis, 84.   "      "     "   ulnaris, 84.   "      "   digit. comm., 85, 87.   "      "     "    I, II, 108.   "      "     "    II brev., 89.   "      "     "    II long., 88.   "      "     "    II prop., 110.   "      "     "    II tert., 89.   "      "     "    III brev., 89.   "      "     "    III long., 89.   "      "     "    III prop., 111.   "      "     "    III, IV, V, 107.   "      "     "    IV brev., 90.   "      "     "    " long., 90.   "      "     "    " prop., 112.   "      "     "    V brev., 90.   "      "     "    " long., 90.   "      "     "    " prop., 113.   "      "   metacarp. digit. III, 90.   "      "      "        "    IV, 90.   "      "   metatars. digit. II, 110.   "      "      "        "    III, 111.   "      "   metatars. digit. IV, 112.   "      "   phal. prop. dig. III, 112.   "      "     "    "     "   IV, ant., 113.   "      "     "    "     "   IV, post., 113.   "      "     "    "     "   V, 90.   "      "     "    "   , 113.   "      "   tarsi ant., 104.   "      "     "   post., 114.   "   gastrocnemius, 102.   "   genioglossus, 66, 281.   "   geniohyoideus, 64.   "   glutaeus, 94.   "   hyo-arytenoideus anterior, 315.   "           "        posterior, 315.   "   hyoglossus, 66, 281.   "   ilio-fibularis, 96.   "   ilio-lumbaris, 74.   "   ilio-psoas, 101.   "   infraspinatus, 79.   "   intercrurales, 75.   "   interossei, 93, 113.   "        "    dorsales, 116.   "   interscapularis, 78.   "   intertransversar. cap. sup., 75.   "       "      "       "   inf., 75.   "       "      "      dorsi, 75.   "   lateralis narium, 60.   "   latissimus dorsi, 72.   "   levator ang. scap., 76.   "       "   bulbi, 57.   "   longissimus dorsi, 72.   "   lumbricales, 108.   "   masseter, 62.   "   nasalis ext., 60.   "   obliquus ext., 67   "       "    inf., 56.   "       "    int., 67.   "       "    sup., 56.   "   obturat., 182.   "   omohyoideus, 65.   "   opponens dig. I, 110.   "       "     "   II, 89.   "       "     "   V, 90.   "   palmaris brev., 87.   "   pectineus, 100.   "   pectoralis, 80.   "   petrohyoideus ant., 65.   "   petrohyoidei post., 66, 315.   "   plantaris, 107.   "   protrahens scap., 76.   "   pterygoideus, 61.   "   pyriformis, 95.   "   quadratus fem., 112.   "   rectus abdom., 67.   "      "   extern. bulbi, 55.   "      "   fem. ant., 95.   "      "   infer. ", 55.   "      "   inter. ", 55.   "      "   intern. major, 97.   "      "   super. ant., 56.   "      "   intern. minor, 98.   "   retractor bulbi, 56.   "   sartorius, 97.   "   semimembranosus, 97.   "   semitendinosus, 100.   "   sphincter ani, 347.   "   sternohyoideus, 64.   "   sternomastoideus, 76.   "   sternoradialis, 82.   "   submaxillaris, 62.   "   submentalis, 63.   "   subscapularis, 78.   "   temporalis, 61.   "   tibialis ant., 104.   "       "    post., 103.   "   transverso-scapularis major, 77.   "        "         "     minor, 77.   "   transversus metacarp., 93.   "        "      plant., 108.   "   triceps femoris, 95.   "   vastus ext., 96.   "      "   int., 96.

Nasal bones, 33.   "   cartilages, 385.   "   glands, 403. Nephrostomes, 336. Nerve, abducens, 171.   "    auditory, 172.   "    brachial, 183.   "    facial, 171.   "    fifth spinal, 187.   "    fourth spinal, 188.   "    glossopharyngeal, 172.   "    hypoglossal, 182.   "    laryngeal, 175.   "    oculo-motor, 167.   "    olfactory, 167.   "    optic, 167, 405.   "    pathetic, 142, 168.   "    palatine, 169.   "    peroneal, 195.   "    pneumogastric, 173.   "    radial, 186.   "    sixth spinal, 188.   "    spinal, 175.   "    structure of, 201.   "    sympathetic, 197.   "    third spinal, 188.   "    tibial trigeminal, 168.   "    vagus, 173. Nerves, 167.   " of Cornea, 408.   " "  ear, 403.   " "  heart, 219.   " "  lungs, 319.   " "  oesophagus, 286.   " "  skin, 378.   " "  stomach, 286. Nervi ciliares, 169. Nervus coccygeus, 189.    "   coraco-clavicularis, 183.    "   cruralis, 189.    "   cut. antibrach. inf., 185.    "   cut. antibrach. sup., 185.    "   cut. dorsi pedis lat., 196.    "   ileo-hypogastricus, 189.    "   peroneus, 195.    "      "    comm. inf., 196.    "      "    lateralis, 196.    "      "    medialis, 196.    "   ramus accessorius, 174.    "     "   anterior, 173.    "     "   auricularis, 172.    "     "   cardiacus, 175.    "     "   cut. axillaris, 183.    "     "   cutaneus dors., 174.    "     "       "    cruris lat., 196.    "     "       "       "   med., 194.    "     "       "       "   post., 194.    "     "       "    fem., 189.    "     "       "    lat., 187.    "     "       "    med., 186.    "     "       "    sup., 186.    "     "   dorsalis, 185.    "     "   gastricus, 175.    "     "   hyoideus, 172.    "     "   hyomandibularis, 172.    "     "   laryngeus, 175.    "     "   lateralis, 185.    "     "   mandibularis, 170.    "     "   maxillaris, 170.    "     "   maxillo-mandibularis, 170.    "     "   muscularis, 187.    "     "   ophthalmicus, 169.    "     "   palatinus, 171.    "     "   pectoralis, 185.    "     "   posterior, 173.    "     "   pulmonalis, 175.    "     "   scapularis, 174.    "     "   subscapularis, 185.    "     "   ulnaris lat., 186.    "     "      "    med., 185.    "   tibialis, 194, 195. Neurilemma, 201. Nictitating membrane, 422. Non-medullated fibres, 202. Nose, 383.   "   skeleton, 27, 383, 385. Nuclear layer, inner, 416.    "      "    outer, 416. Nucleus abducens, 146.    "    auditory, 144.    "    centralis, 144.    "    magnus, 147, 152.    "    medullae oblongatae, 144.    "    pneumogastric, 146.    "    trigeminal, 145.

Oculo-motor nerve, 167.     "       nucleus, 151. Oesophageal glands, 283. Oesophagus, 282. Olfactory nerve, 167. Omosternum, 36. Operculo-angulare, 35. Operculum, 25. Optic chiasma, 153, 155, 167.   "   commissure, 154.   "   fibre layer, 414.   "   lobes, 149.   "   nerve, 167, 405.   "   tracts, 152. Os articulare, 35.  " capitato-hamatum, 45.  " cuboideum, 51.  " cuneiformia, 52.  " en ceinture, 27.  " lunatum, 44.  " multangulum maius, 45.  "      "      minus, 45.  " naviculare of foot, 51.  "      "     of hand, 45.  " occipitale basilare, 23.  "      "     superius, 23.  " pyramidale, 44. Ostium abdominale, 304, 345. Outer nuclear layer, 416. Ovaries, 344. Oviducts, 304, 345.

Palatine artery, 224.     "    bones, 33.     "    nerves, 169. Pancreas, 300. Papilla acustica lagenae, 400. Papillae of skin, 370.     "    of tongue, 380. Parasphenoid, 26. Pars basilaris cochleae, 400.   "  commissuralis, 147, 152.   "  media, 135.   "  neglecta, 400.   "  peduncularis, 143, 152. Partes condyloideae, 23. Pathetic nerve, 142, 168. Pectoral lymph-sac, 255.    "     septum, 253. Pelvis, 47. Pericardium, 213. Periganglionic glands, 180. Perilymphatic space, 393. Perineal septum, 253. Peritoneum, 303. Phalanges of foot, 52.   "   "   of hand, 47. Pia mater, 162. Pigment of cerebellum, 149.    "    "  cord, 141.    "    "  hemispheres, 160.    "    "  liver, 299.    "    "  medulla, 148.    "    "  optic lobes, 152.    "    "  thalamencephalon, 155.    "    "  skin, 369. Pigment-layer, 419. Pineal body, 155. Pituitary body, 154, 156. Plexus, Auerbach’s, 292.    "    lateralis, 165.    "    Meissner’s, 291. Pneumogastric nerve, 146, 173.    "     "    nucleus, 146. Pons Varolii, 149. Portal systems, 247.    "   vein, 297. Posterior chamber, 420. Pre-arytenoid cartilages, 314. Precoracoid, 40. Premaxillary bones, 33. Processes, articular, 17.     "      spinous, 17.     "      transverse, 17. Processus coracoideus, 40.     "     coronoideus, mandible, 34.     "        "   "     radio-ulnar, 43.     "     mastoideus, 24.     "     zygomaticus, 30. Prootic bones, 24. Pterygoid bones, 31. Pubes, 49. Pulmo-cutaneous arch, 230. Pulp-cavity, 279. Purkinge’s cells, 148.

Radio-ulnar, 43. Rami communicantes, 181, 199. Rana aquatica, 3.   "  esculenta, 4.   "  flaviventris, 7.   "  gibbosa, 3.   "  innoxia, 3.   "  oxyrhinus, 7, 9.   "  rubeta, 3.   "  temporaria, 7. Receptaculum seminis, 337. Recessus utriculi, 396. Remak’s ganglion, 220. Renal arteries, 333.   "   portal vein, 332.   "   veins, 333. Reproductive organs, 341. Retina, 414. Retinal pigment, 419. Ritter’s fibres, 418. Rods and cones, 416. Roots of spinal nerves, 175. Round bundle, 154, 159.

Saccus endolymphaticus, 395, 398.    "   fenestra ovalis, 395.    "   perilymphaticus, 395. Sacrum, 19. Scapula, 37. Sciatic artery, 236.    "    nerve, 192.    "    plexus, 191. Sclerotic coat, 405. Semicircular canal, ant., 396.   "     "      ",   ext., 398.   "     "      ",   post., 398. Septa, of lymph-sacs, 252. Septum medium, 139. Serous glands of skin, 372. Shoulder-girdle, 37.     "   -joint, 42. Sinus, superior, 383. Sinus venosus, 214. Skeleton, 15.     "    of nose, 27, 383, 385. Skin, 367. Skull, 21. Small intestine, 286. Sphenethmoid, 27. Spinal cord, 135.    "   ganglia, 177.    "   nerves, 135, 175, 181.    "   roots of, 175. Spinous processes, 17. Spleen, 302. Squamosal bones, 30. Sternum, 36. Styloid cartilage, 25. Submaxillary lymph-sac, 255. Substantia reticulosa, 138. Sulcus longitud. inf., 135.    "       "     sup., 135. Superior sinus, 383. Supplemental toe, 5, 47, 374. Supra-femoral lymph-sac, 260.   "      "    septum, 259. Suprascapula, 37. Suprastapedial, 26, 390. Suspensorium, 30. Sylvian aqueduct, 150. Sympathetic system, 197. Symphysis pubis, 48. Systemic arch, 226.

Tactile sensation, organs, 377. Taste-organs, 380. Teeth, 278. Tegmentum vasculosum, 395, 402. Temporary papillae, 370. Testis, 341. Thalamenoephalon, 153. Thalamus-tubercinereum strand, 154, 155, 159. Third ventricle, 153. Thymus gland, 320. Thyroid gland, 322. Tibio-femoral septum, 260. Tibio-fibula, 49. Toes, 5, 47, 374. Tongue, 280. Tonsils, 323. Touch-corpuscles, 379.   "  -spots, 378. Transverse processes, 17. Trigeminal nerve, 168.     "      nucleus, 145. Trochlear nerve, 168. Truncus arteriosus, 216. Tuberculus maius, 42. Tympanic membrane, 389.     "    ring, 26. Tympanum, 389, 390.

Upper nasal gland, 386. Ureters, 337. Urinary bladder, 338.    "    organs, 332. Uriniferous tubes, 334. Urino-genital system, 330. Urostyle, 21. Utricle, 396.

Vagus, 173. Valvula cerebelli, 148. Vasa efferentia, 341.   "  recta, 412, 413. Vein, anterior abdominal, 248.   "       "    caval, 241.   "       "    orbital, 245.   "       "    tibial, 250.   "   brachial, 246.   "   cardiac, 249.   "   caval anterior, 241.   "     "   posterior, 246.   "   cutaneous, 244.   "   dorso-lumbar, 248.   "   external jugular, 241.   "   facial, 245.   "   femoral, 249.   "   gastric, 249.   "   haemorrhoidal, 249.   "   hepatic, 247, 297.   "   hepatic portal, 249.   "   iliac, 247.   "   innominate, 242.   "   internal jugular, 243.   "   intestinal, 249.   "   jugular, external, 241.   "       "    internal, 243.   "   lingual, 241.   "   mandibular, 242.   "   median orbital, 243.   "   nasal, 245.   "   ophthalmic, 412.   "   orbital anterior, 245.   "      "    median, 243.   "      "    posterior, 245.   "   ovarian, 247.   "   oviducal, 248.   "   portal, 297.   "   posterior caval, 246.   "   posterior orbital, 245.   "   pulmonary, 241.   "   radial, 246.   "   renal, 247, 333.   "   renal portal, 332.   "   sciatic, 247, 250.   "   spermatic, 247.   "   splenic, 249.   "   subclavian, 244.   "   subscapular, 244.   "   ulnar, 246.   "   vertebral, 244. Veins, 241. Vena bulbi anterior, 222.   "    "   superior, 412.   "    "   posterior, 222.   "  spinalis anterior, 164.   "     "     posterior, 165.   "     "     superior, 164. Ventral lymph-sac, 255. Ventral nucleus, 155.    "    septum, 252. Ventricle of heart, 215. Ventricles of brain, 153.     "      of larynx, 316. Vertebrae, 16.    "      structure of, 20. Vertebral column, 16. Vessels of brain, 162.    "    of liver, 297. Vitreous body, 420. Vocal cords, 315.   "   sacs, 320. Vomerine teeth, 276. Vomers, 34.

Webs, 5, 275. Wrist-joint, 45.

THE END.

[Illustration:

The Anatomy of the Frog.

Plate I.

University Press Oxford. ]

[Illustration:

The Anatomy of the Frog.

Plate II.

University Press Oxford. ]

_TRANSLATIONS OF FOREIGN BIOLOGICAL MEMOIRS._

I.

*The Physiology of Nerve, of Muscle, and of the Electrical Organ.* Edited by J. BURDON-SANDERSON, M.D., F.R.SS. L. & E., Waynflete Professor of Physiology in the University of Oxford. Medium 8vo., cloth, price 21_s._

II.

*The Anatomy of the Frog.* By Dr. ALEXANDER ECKER, Professor in the University of Freiburg. Translated, with numerous Annotations and Additions, by GEORGE HASLAM, M.D.; and profusely Illustrated.

III.

*Contributions to the History of the Physiology of the Nervous System.* By Professor CONRAD ECKHARD. Translated by Miss EDITH PRANCE. _In Preparation._

IV.

*Essays upon Heredity and Kindred Biological Problems.* By Dr. AUGUST WEISMANN, Professor in the University of Freiburg-in-Breisgau. Authorised Translation edited by EDWARD B. POULTON, M.A., F.L.S., F.G.S., Tutor of Keble College, Lecturer in Natural Science, Jesus College, Oxford; SELMAR SCHÖNLAND, PH.D., Sub-Curator of the Fielding Herbarium in the University of Oxford; and ARTHUR E. SHIPLEY, M.A., F.L.S., Fellow and Lecturer of Christ’s College, and Demonstrator of Comparative Anatomy in the University of Cambridge. Medium 8vo., cloth, price 16_s._

Oxford

AT THE CLARENDON PRESS

LONDON: HENRY FROWDE

OXFORD UNIVERSITY PRESS WAREHOUSE, AMEN CORNER. E.C.

*Spelling corrections*:

brev → brevis deltoides → deltoideus Duges → Dugès entricles → ventricles evator → levator Labratoire → Laboratoire longitudina → longitudinal Ponicaré → Poincaré resistent → resistant respectiveyl → respectively Thanoffer → Thanhoffer Tranverse → Transverse Trevianus → Treviranus

*Spelling inconsistencies*:

Darmkanal/Darmcanal maior/major maius/majus Monro/Monroe/Monroi Entwickelung & Entwicklungsgeschichte (with and without initial capitals)