PART 1.

THE HEART AND BLOOD-VESSELS.

I. THE HEART.

(The original arrangement of this section has been modified.)

The heart is situated in the middle line above the central portion of the shoulder-girdle and _M. sternohyoideus_, and below the oesophagus; the apex is directed backwards and lies between the lobes of the liver, the base is directed forwards and lies a short distance behind the larynx. The heart is surrounded by the pericardium.

A. The *Pericardium* [is a very thin membranous sac, which completely encloses the heart; it is attached, at some distance, to the large vessels passing to and from the heart, and has inserted into it some fibres of the _M. obliquus abdominis internus_ (see page 70). A fold of the pericardium extends from the dorsal surface to the truncus arteriosus, and through it courses the vena cardiaca.

[Illustration: Fig. 132.

The heart and blood-vessels, seen from the ventral surface; after Howes.

_AC._ Left anterior caval vein. _C′._ Carotid arch. _LA._ Left auricle. _P′._ Right pulmo-cutaneous arch. _RA._ Right auricle. _S′._ Left systemic arch. _TA._ Truncus arteriosus. _V._ Ventricle. ]

The pericardium is a connective-tissue membrane, and is lined on either side with endothelium, which is in part ciliated (Leydig); the endothelium of the inner surface is continued on to the heart and so forms a closed lymph-sac. The pericardium is more or less pigmented, and contains both vessels and nerves; it may contain fat-cells].

B. The *Heart*.

[The heart is a hollow muscular organ, composed of: (1) two auricles, forming the wider anterior portion; (2) the ventricle, placed behind the auricles; (3) the sinus venosus, situated dorsally; and (4) the truncus arteriosus, lying ventrally. Examined while still living, the auricles are seen to be much darker in colour than the ventricle, due to the blood being seen through their thinner walls; between the auricles and the ventricle is a distinct groove, the auriculo-ventricular groove. The whole organ is more or less pigmented, especially the ventricle (_R. temporaria_ has much less pigment).]

[Illustration: Fig. 133.

The heart, seen from above, and dissected to show the opening from the Sinus venosus to the right auricle; after Howes.

_C′._ Right carotid arch. _IC._ Posterior caval vein. _LA._ Left auricle. _P′._ Right pulmo-cutaneous arch. _PV._ Pulmonary vein. _RA._ Right auricle. _S′._ Right systemic arch. _SV._ Sinus venosus. _SV′._ Opening of Sinus venosus into the right auricle. _V._ Right anterior caval vein. ]

*a.* The *Sinus venosus* (_Sinus venarum cavarum_), (Fig. 133 _SV._) is a thin-walled sac lying on the dorsal surface of the heart, and very slightly to the right side (Hoffmann). It is somewhat triangular in form, receiving an anterior caval vein at each anterior angle (_V._), and the posterior caval vein (_IC._) at the posterior angle. The ventral wall has a transverse opening (_SV′._), by which it communicates with the right auricle; the opening possesses two valves, an anterior and a posterior, and is placed close to the auricular septum.

*b.* The *auricles* [are not always separated, as the septum which usually brings about the separation is in some cases incomplete, and in rare instances appears to be absent (Hoffmann)]; according to Ecker, the auricular septum is sometimes placed so far to the left side that it appears to be absent (Fig. 135). The septum is attached to the walls of the auricles so as to form two distinct cavities, which communicate at the auriculo-ventricular opening, where the septum has a free concave border (Fig. 134). The right auricle is much larger than the left, and receives the systemic venous blood from the sinus venosus by the opening (Figs. 133 and 134 _SV._) already described. The left auricle receives the blood from the lungs by the pulmonary vein (Fig. 133 _PV._), which opens into the auricle near the septum (Fig. 134 _PV._): [the openings from the sinus venosus and from the pulmonary vein may be so closely approximated as to be separated by the septum only. The septum is much thinner than the auricular walls]. Both auricles open into the ventricle by the auriculo-ventricular opening (Fig. 134).

[Illustration: Fig. 134.

The frog’s heart seen from the ventral surface, and dissected so as to show its structure. The ventral walls of the truncus arteriosus and of the auricles and ventricle have been removed. From a drawing by Mr. Hurst.

_A._ Auriculo-ventricular aperture and valve. _B._ Aperture leading from ventricle to truncus arteriosus. _C._ Left carotid arch. _LA._ Left auricle. _P._ Left pulmo-cutaneous arch. _P′._ Style passed down right pulmo-cutaneous arch into the truncus arteriosus, _T._ _PV._ Opening of pulmonary vein. _RA._ Right auricle. _S._ Left systemic arch. _SA._ Septum atriorum. _SV._ Opening of Sinus venosus into right auricle. _V._ Ventricle. ]

*c.* The *ventricle* (Figs. 132, 134, and 136 _V._), examined while still living, is seen to be bluntly conical in shape and darker on the left side than on the right; this is due to the ventricular wall of the right side, near the truncus arteriosus, being somewhat thinner. The inner wall is not smooth but possesses muscular ridges (_Trabeculae_). At its base the ventricle communicates with the auricles by the auriculo-ventricular opening (Figs. 134 and 136), and with the truncus arteriosus by a separate opening (Fig. 134 _A._). The ventricle is lined by a layer of endocardial endothelium.

[Illustration: Fig. 135.

Dissection of a case in which the auricular septum is placed more to the left than is normal.

_S_ Septum. _SS_ Left auricle. _V_ Opening into the Sinus venosus. ]

[Illustration: Fig. 136.

Dissection of the heart from the left side; after Howes.

_A._ Auriculo-ventricular opening. _AC._ Anterior caval veins. _IC._ Posterior caval vein. _LA._ Left auricle. _PV._ Pulmonary vein. _RA._ Right auricle. _SV._ Sinus venosus. _TA._ Truncus arteriosus. _V._ Ventricle. ]

The *auriculo-ventricular opening* (Fig. 134 _A._) is a large aperture guarded by two valves, a dorsal and a ventral: each valve is formed by a reduplication of the endothelium, and contains a small amount of connective-tissue; its free margin is bound down by a number (about twelve) of fibrous cords, the _chordae tendineae_, which are attached by their posterior extremities to the trabeculae.

*d.* The *truncus arteriosus* (Figs. 132 _TA._, 134 _A._) arises at the base of the ventricle, on the right side of its ventral surface, then passes forwards and to the left, across the auricles, to reach their anterior border near the median line, where it divides to form two vessels.

Internally it is incompletely divided into two compartments by a spiral valve (Fig. 134); the valve is attached to the dorsal surface and is free ventrally: when the vessel is fully dilated (artificially), the valve extends two-thirds of its diameter. The opening of the vessel into the ventricle is guarded by two semilunar valves (Fig. 134 _A._), the free margins of which are bound to the inner surface of the tube by _chordae tendineae_. The distal extremity has a semi-lunar valve in the left compartment (Fig. 134), which is attached by a delicate band to the spiral valve (Ecker).

C. *The minute structure of the Heart.*

[The heart consists chiefly of muscle, but possesses also nerve-fibres, nerve-cells, endothelium, and connective-tissue; the truncus arteriosus has, in addition, blood-vessels.

*a.* The *muscular structure* of the heart.

(1) The *arrangement* of the *muscle-fibres* varies in the different portions of the heart. That of the ventricle will be easily understood by reference to Fig. 137. A layer of circular fibres (_CM_) extends round the whole ventricle, and from it more or less radial or transverse bands (_TM_, also Fig. 138 _TM_) pass inwards; these, in the apical portion of the ventricle, seem to extend almost transversely across; towards the base they are directed onwards and forwards towards the auricles. Of these bands some, near the apex, can be traced directly to the opposite side, others join the wall more anteriorly, and still others join bands of muscular fibres (_LM_), which may be described as longitudinal, and form the _Musculi papillares_. In the anterior portion of the ventricle the same arrangement holds good, but is modified to form a central cavity; still more anteriorly, at the junction of auricles and ventricle, the trabecular structure is much less apparent, the fibres being closer and mainly circular.

[Illustration: Fig. 137.

I. Transverse section through the junction of the hinder and middle thirds of the ventricle of _R. temporaria_. II. Transverse section through junction of middle and anterior thirds of the same heart. Occ. I, Syst. 1, Leitz. The heart was freely distended[62] with dilute spirit, and so hardened.--G. H.

_CC_ Central cavity. _CM_ Circular muscle. _LM_ Longitudinal muscle. _TM_ Transverse muscle. ]

[Footnote 62: The base of the ventricle measured, when distended, 8 mm. by 5 mm.]

In the auricles the muscular fibres are chiefly arranged in circular rings which cross one another; on the inner surface, however, traces of an arrangement similar to that in the ventricle may be made out. In the heart, from which the sections in Fig. 137 were drawn, transverse bands (cut longitudinally), 0.33 mm. in length, were numerous; their central ends terminated in bands, the fibres of which were cut transversely. The auricular septum (Fig. 141 a _M_) also possesses muscular fibres which cross one another in its substance.

The fibres of the truncus arteriosus resemble those of an ordinary artery; those of the sinus venosus are arranged in rings, mostly transverse, but others oblique, and a few longitudinal.]

(2) The *structure* of the *cardiac muscle-fibres* (Figs. 138 and 141 a).

[The cardiac muscle of the frog consists of spindle-shaped cells, which as Pohl-Pincus pointed out, are of two kinds; the main difference between the two being in the size of the nucleus, which is much broader in one than in the other.

[Illustration: Fig. 138.

Portion of a transverse section through the middle of the ventricle of _R. temporaria_. From same heart as the sections in Fig. 136. Oc. I. Syst. 7, Leitz.--G. H.

_A_ Rod-shaped nuclei of muscle fibre. _B_ Oval nuclei of muscle fibre. _CM_ Circular layer of muscle. _CT_ Connective-tissue. _E_ Endothelium of the epicardium. _TM_ Transverse bands of muscle. ]

α. Cells with a broad nucleus (Fig. 138 _B_): the nucleus is lenticular or egg-shaped, 4 to 7 µ broad, 8 to 14 or 18 µ long; the ratio of length to breadth being 1 : 2.

β. Cells with a narrow nucleus (Fig. 138 _A_): the nucleus is rod-shaped, 2·5 to 3·5 µ broad and 25 to 43 µ in length. The ratio of length to breadth varying from 1 : 8 to 1 : 16. These cells are more frequent in the right half of the base of the ventricle than the former variety. In the trabeculae the second variety is more numerous (Pohl-Pincus).

The muscle-fibre may be simple (Fig. 141 a _M_) or possess branches (Fig. 138); the fibres are all more or less spindle-shaped, and striated transversely and longitudinally, but possess no sarcolemma. The protoplasmic contents of the cell are finely granular; the nucleus much more coarsely granular and possessing one or more distinctly marked nucleoli. The striations are due to the presence of a network, which has been carefully described by Messrs. B. Melland and C. F. Marshall[63], and is similar to that of ordinary voluntary muscle (see histology of muscle).]

[Footnote 63: I have had opportunity of examining Mr. Marshall’s slides and have convinced myself of the correctness of his observations.]

*b.* The *nerves* of the *heart*.

The nervous supply of the heart is derived from the sympathetic system and from the cardiac branches of the pneumogastric nerve; the course of which has already been traced (page 175) to the roots of the anterior caval veins, where they form a simple plexus by means of a connecting link (Fig. 139). The plexus possesses nerve-cells and sends off two nerves into the auricular septum; the one (_d_) lies dorsally and is shorter and thicker than the other (_v_), which lies ventrally in the septum. They course backwards to the posterior border of the septum, and there distribute fine branches to the base of the ventricle and surrounding parts.

[Illustration: Fig. 139.

Course of the cardiac nerves in the auricular septum.

_d_ Dorsal nerve. _v_ Ventral nerve. ]

[In the whole of their course in the heart they have numerous nerve-cells, either imbedded between their fibres or attached to the nerves and their branches.

The nerve-fibres are both medullated and non-medullated. The nerve-cells (Figs. 139, 140, 141) are usually oval, and are unipolar or rarely bipolar; sometimes two cells exist in the same envelope, forming the ‘twin-cells’ of Dogiel (Fig. 141 b II). According to the recent observations of Lavdowsky and Dogiel each cell receives one medullated fibre and gives off a fine non-medullated fibre; the two run together for a short distance, after which the non-medullated fibre separates to supply muscle-fibres.

[Illustration: Fig. 140.

Group of nerve-cells on the cardiac nerve, from the auricular septum. Stained with picrocarmine. Occ. III, Syst. 3, Hartnack; after Dogiel.

_F_ Fibres of the cardiac nerve. _G_ Nerve-cells. ]

Two large clusters of nerve-cells have received special names.

*Remak’s ganglion* is a large group of nerve-cells in the wall of the sinus venosus.

*Bidder’s ganglion* is formed, collectively, by groups of cells in the auriculo-ventricular groove, the chief groups being attached to the two cardiac nerves.

No nerve-cells have been discovered behind that portion of the ventricle near the auriculo-ventricular groove, nor has a direct connection between the cells or their processes with the fibres of the pneumogastric nerve been made out.

Nerve-fibres have been described as existing in all parts of the ventricle and being connected with the muscle-fibres (Openchowsky and others); this cannot, as yet, be accepted as proved.

The truncus arteriosus also possesses nerve-fibres and nerve-cells (Pagliani, Löwit, and others), but their arrangement seems to be very irregular. Löwit did not succeed in finding the nerve-cells in all cases examined; and Engelmann denies their occurrence.]

*c* and *d*. [The *endothelium* and *connective-tissue* of the heart.

The connective-tissue of the heart exists only in very small quantity. A fine layer on the outer surface of the ventricle, especially towards the auriculo-ventricular groove, can easily be seen (Fig. 138 _CT_); the various valves, the auricular septum, and more particularly the truncus arteriosus, all contain connective-tissue. In the latter part the spiral valve is wholly formed of this tissue.

[Illustration: Fig. 141 a.

Small group of nerve-cells from the auricular septum. Stained with picrocarmine and silver nitrate, after Dogiel.

_E_ Endothelium (endocardium). _G_ Nerve-cells. _M_ Muscle-fibres. _N_ Nucleus. _N_′ Nucleolus. ]

[Illustration: Fig. 141 b.

Isolated nerve-cells from frog’s heart. I. Usual form of nerve-cell. II. ‘Twin-cell.’

_C_ Capsule. _N_ Nucleus. _N_′ Nucleolus. _P_ Process. ]

The whole of the inner surface is lined with endothelium (endocardium), which covers the various trabeculae; the external surface of the heart is likewise covered with an epicardial layer of endothelium (Fig. 138 _E_).]

[Illustration: Fig. 142.

Arteries and veins of the Truncus arteriosus of Bufo vulgaris, after Hyrtl.

_a_ Arteria bulbi. _b_ Truncus arteriosus. _h_, _i_ Hepatic portal veins. _t_ Right and left synangium. _v_ Vena bulbi anterior. _vi_ Left innominate vein. _vc_ Vena bulbi posterior (V. cardiaca). _A_ Right auricle. _A_′ Left auricle. _V_ Ventricle. ]

*e.* The blood-supply to the heart.

With the exception of the _truncus arteriosus_, no part of the heart possesses blood-vessels (Hyrtl). [The _truncus arteriosus_ (Fig. 142 _b_) has a rich anastomosis, which receives its blood by the _arteria bulbi_ (_a_), a branch of the carotid arch. Two veins connect this anastomosis with the systemic veins, and with the hepatic portal veins: the former, _vena bulbi anterior_ (_v_), passes over the auricles to open into the left innominate vein (_vi_); the latter, the _vena bulbi posterior_ (_vc_) or _vena cardiaca_, as it is more usually named, passes from the _truncus arteriosus_ in a fold of pericardium, and then courses backwards to open into the anterior-abdominal vein.]

II. THE ARTERIES.

(The original arrangement of this section has been modified.)

The _Truncus arteriosus_ divides to form two vessels (Figs. 132, 134); each of these is divided by two partitions into three compartments, which after a short course together separate to form three distinct vessels, the carotid, systemic, and pulmo-cutaneous arches.

*1.* The *carotid arch* (_Canalis carotico-lingualis_, Brücke; _Ductus caroticus_), (Fig. 143 _I_) is the most anterior of the three arches: it winds round the side of the oesophagus as far as the carotid gland, where it divides to form two branches; the right carotid arch gives off a small branch to the _Truncus arteriosus_, the _Arteria bulbi_ (see above).

[Illustration: Fig. 143.

Schema of the arterial system of Rana esculenta.

_A_ Dorsal aorta. _c_ Cutaneous artery. _ca_ Carotid artery. _d_ Carotid gland. _ic_ Iliac arteries. _ie_ External iliac artery. _ii_ Internal iliac artery. _J_ Mesenteric artery. _l_ Lingual artery. _o_ Occipital artery. _ov_ Occipito-vertebral artery. _P_ Pulmonary artery. _s_ Subclavian artery. _T_ Truncus arteriosus. _ug_ Urinogenital arteries. _v_ Vertebral artery. _I_ Carotid arch. _II_ Systemic arch. _III_ Pulmo-cutaneus arch. ]

The *carotid gland* (Fig. 144 _c_′) is a dilated portion of the vessel. The interior contains bands or trabeculae of muscle, which give its walls a more or less spongy structure; the muscle-fibres are not transversely striated (Hoffmann).

*a.* The *lingual artery* (_Arteria lingualis_, _Arteria hyoidea-lingualis_, _Arteria hyoidea_), (Figs. 143 _l_, 144 _L_) arises by two roots from the inner surface of the carotid gland, and courses forwards and inwards, supplying branches to the thyroid gland and the _Musculi geniohyoidei_, to the ventral surface of the hyoid; another continues forwards on the outer border of the _M. hyoglossus_ to supply branches to the hyoid and tongue.

*b.* The *carotid artery* (_Arteria carotis communis_), (Figs. 143 _ca_, 144 _c_″) arises by several roots from the outer wall of the carotid gland; and passes over the _Musculus petrohyoideus I_ to the anterior end of the oesophagus, round which it courses towards the vertebral column, and then runs forwards to the base of the skull. The artery then courses forwards, lying immediately above the mucous membrane and underneath the transverse arm of the parasphenoid, which it crosses about midway between its back and external end; [at this point the artery gives off two palatine arteries, then ascends in the orbit to the origin of the _M. pterygoideus_, and divides into two branches, the internal carotid artery and the ophthalmic artery]. The branches are:--

(1) The pharyngeal artery (_Arteria pharyngea ascendens_), (Fig. 145 _p_) which runs towards the opening of the Eustachian tube, distributes branches to the pharynx, and anastomoses with the _Arteria pharyngeo-maxillaris_ of the cutaneous artery, and with the _Ramus inframaxillaris_ of the occipital artery.

[Illustration: Fig. 144.

Right carotid gland.

_c_ Carotid arch. _c_′ Carotid gland. _c_″ Carotid artery. _L_ Lingual artery. ]

(2) [The posterior palatine artery (_Arteria palatina posterior_, Virchow) immediately divides into a number of small twigs to supply the mucous membrane of the hinder and outer parts of the gums.]

(3) The anterior palatine artery (_Arteria palatina anterior_, Virchow; _Arteria palatina_, Ecker), (Fig. 145 _p_′) runs forwards, between the _Musc. levator bulbi_ and the mucous membrane, with the _Ramus palatinus_ of the trigeminal nerve. [On reaching the palatine bone, it curves outwards to the outer anterior angle of the orbit, where it gives off a branch backwards along the upper jaw to the hinder portion of the orbit.] In its course it supplies twigs to the surrounding tissues, but chiefly to the mucous membrane and Harder’s gland.

[Illustration: Fig 145.

Arterial system of _Rana esculenta_.

_A_ Dorsal aorta. _Ad_ Right systemic arch. _As_ Left systemic arch. _c_ (opposite fore-limb) Carotid artery. _c_ (in abdomen) Coeliac artery. _cm_ Cutaneous artery. _e_ Lingual artery. _H_ Heart. _H_′ Harderian gland. _L_ Liver. _Lu_ Lung. _m_ Mesenteric artery. _M_ Stomach. _M_′ Spleen. _o_ Ophthalmic artery. _p_ Pharyngeal artery. _p_′ Anterior palatine artery. _S_ Subclavian artery. _I_ Carotid arch. _II_ Systemic arch. _III_ Pulmo-cutaneous arch. ]

(4) The internal carotid artery (_Art. cerebralis_, Virchow); see Arteries of Brain, p. 162.

(5) The ophthalmic artery (_Art. ophthalmica_), (Fig. 145 _o_) [is larger than the internal carotid artery at this point; it crosses the origins of the _M. rectus externus_ and of the _M. retrahens bulbi_ and reaches the optic nerve; the artery then runs forwards along the under surface of this nerve and of the eyeball, lying close to the sclerotic coat as far as a little beyond the equator, where it pierces the sclerotic coat so obliquely that the choroid coat is only reached at the ciliary processes. In its course the artery supplies:--

α. Muscular branches, given off at the point where the artery reaches the eyeball.

β. Two arteries (_AA. ciliares_) to the choroid, given off at the same point as the foregoing.

γ. Two arteries to the iris.

δ. The _Art. hyaloidea_, the terminal portion of the ophthalmic artery. (For further description of these vessels, see Eye.)].

*2.* The *systemic arch* (_Ductus aorticus_), (Figs. 132, 143, and 145 _II_) is the middle arch of the three; it arises from the middle canal of the _Ductus arteriosus_, and winds obliquely round the oesophagus between the _MM. petrohyoidei I_ and _II_ towards the vertebral column, which it reaches at about the level of the sixth vertebra. The right systemic arch is continued as the dorsal aorta, the left arch communicates with it merely by a small opening, and is then continued as the coeliaco-mesenteric artery.

Branches of the systemic arch:--

*a.* The *laryngeal artery* (_Arteria laryngea_), (Fig. 146 _lg_) arises from the inner border of the systemic arch before it reaches the oesophagus; it passes forwards and inwards to be distributed in the larynx and pharynx. According to Brücke this artery possesses a valve at its point of origin.

[Illustration: Fig. 146.

Transverse section at level of the larynx.

_C_ Carotid gland. _G_ Glottis. _lg_ Laryngeal artery. _S_ Subclavian artery. _I_ Carotid arch. _II_ Aortic arch. ]

*b.* The *oesophageal arteries* (_Arteriae oesophageae_) pass from the upper part of the arch to the dorsal surface of the oesophagus.

*c.* The *occipito-vertebral artery* (Ecker), (_Art. occipito-vertebralis_), (Fig. 147 _o_, _v_) [arises from the systemic arch immediately in front of the transverse process of the second vertebra, and ascends immediately in contact with the body of the first vertebra, which it separates from the _MM. intertransversarii capitis_ and the sympathetic cord]. Immediately under the most anterior portion of the _M. longissimus dorsi_ the artery divides into two branches, the vertebral and occipital arteries:--

(1) The *vertebral artery* (_Arteria vertebralis_ or _supra-vertebralis_) (Fig. 147 _v_) courses backwards lying on the transverse processes of the vertebrae and on the _MM. intertransversarii_, under cover of the _M. longissimus dorsi_. In this course it is close to the oblique processes, and may even be partially covered by these; it extends beyond the sacrum, and gives off:--

α. The _Rami spinales_, which pass through the intervertebral foramina to the spinal cord (see Arteries of Spinal Cord, p. 162).

[Illustration: Fig. 147.

Dissection to show the occipito-vertebral and the cutaneous arteries.

The skin of the back has been divided by a median incision and drawn to either side; the right arm dislocated and removed through the opening in the skin (at _A_). On the left side the extensor muscles of the back have been removed.

_c.m._ Cutaneous artery. _c.p._ Arteria cutanea pectoris. _o_ Occipital artery. _s_ Scapular artery. _v_ Vertebral artery. ]

β. The _Rami dorsales_; these supply the muscles of the back and send branches to the skin, which accompany the cutaneous branches of the spinal nerves through the _Saccus lymphaticus cranio-dorsalis_.

γ. The _Rami intercostales_ are distributed in part to the _MM. intertransversarii_; other twigs pass ventrally to the periganglionic glands; the longest branches accompany the anterior divisions of the spinal nerves to the muscles and skin of the belly (Fig. 145).

(2) The *occipital artery* (_Arteria occipitalis_), (Figs. 147 and 148 _o_), the anterior branch of the occipito-vertebral artery, pierces the _M. longissimus dorsi_; then courses forwards under cover of the _Fascia dorsalis_ and upon the _M. temporalis_, and divides, behind the eyeball [at the anterior border of the _M. temporalis_, Virchow], into two branches:--

α. The _Ramus orbito-nasalis_ (Fig. 148 _on_) accompanies the ophthalmic nerve along the wall of the cranium, and passes through the sphenethmoid, with the nasal branch of the ophthalmic nerve, to the nose, where it divides into two branches supplying the mucous membrane of the nose. In its course through the orbit the artery supplies branches to the Harderian gland and neighbouring parts, and anastomoses with the ascending branch of the _Arteria palatina_.

β. The _Ramus maxillaris communis_ (_Art. temporalis_, Virchow), (Fig. 148 _m_) runs downwards and outwards along the anterior border of the _M. temporalis_, and passes under the anterior arm of the squamosal bone to course backwards on the upper jaw. At this point the _Ramus maxillaris superior_ (_m_′) is given off. The main artery continues its backward course to the tympanic membrane, where it divides into its three terminal branches:--

[Illustration: Fig. 148.

Branches of the occipito-vertebral and cutaneous arteries in the head; side view. The skin (_H_) has been reflected downwards.

_c.m._ Cutaneous artery. _l.a._ M. levator scapulae. _m_ Art. maxillaris communis. _m_′ Art. maxillaris superior. _m_″ Art. maxillaris inferior. _o_ Occipital artery. _on_ Art. orbito-nasalis. _p.m._ Art. pharyngo-maxillaris. _v_ Vertebral artery. ]

[(1) The _Ramus maxillaris superior_ (_AA. maxillares superiores_, Virchow), usually not a single artery but a number of small twigs, which supply the space between the eye and the upper jaw.

(2) A small ascending branch to the tympanic membrane (Virchow).

(3) A _Ramus auricularis_ (Virchow), which forms a rich anastomosis on the hinder wall of the tympanic cavity, and supplies a twig to the tympanic membrane. This passes from the upper border of the membrane to the point of attachment of the _Columella auris_ (extrastapedial), round which it forms a circular anastomosis. The _Ramus auricularis_ also anastomoses with the cutaneous artery.

[Illustration: Fig. 149.

Dissection to show the occipito-vertebral and the cutaneous arteries.

The skin of the back has been divided by a median incision and drawn to either side; the right arm dislocated and removed through the opening in the skin (at _A_). On the left side the extensor muscles of the back have been removed.

_c.m._ Cutaneous artery. _c.p._ Arteria cutanea pectoris. _o_ Occipital artery. _s_ Scapular artery. _v_ Vertebral artery. ]

(4) A branch passing inwards to the fat-body, and lying immediately in front of the deltoid muscle (Virchow).

(5) A small branch running on to the inner surface of the angle of the jaw and then forwards (Virchow).

(6) A larger vessel, the _Ramus maxillaris inferior_ (Fig. 148 _m_″), which arises from the _Ramus maxillaris superior_ under cover of the tympanic membrane, and accompanies the _Ramus mandibularis_ of the trigeminal nerve through the _M. masseter_, or between this muscle and the _M. temporalis_ to the mandible, and then courses forwards to the chin. A large cutaneous branch is given off half-way along the floor of the mouth. The artery gives off many small twigs to supply the neighbouring structures.]

3. The *pulmo-cutaneous arch* (_Ductus pulmo-cutaneus_), (Figs. 132 143, and 145 _III_) is the hindmost (fifth embryonic) of the three persistent arches; it passes upwards and forwards on the oesophagus, and at the level of the carotid gland divides into two branches, the pulmonary artery and the cutaneous artery.

a. The *pulmonary artery* (_Arteria pulmonalis_) runs backwards to the root of the lung, along the outer surface of which it is continued in a sinuous course. It supplies the lung.

b. The *cutaneous artery* (_Arteria cutanea magna_), (Fig. 149 _c.m._) [passes along the deeper surface of the _M. petrohyoideus III_ until near the prootic bone; in this course it travels forwards, outwards, and upwards, crosses the outer border of the muscles, and appears between the _M. levator anguli scapulae_ and the _M. sternocleidomastoideus_. At this point the artery curves sharply round to reach the angle of the jaw, the hinder border of the _M. depressor maxillae inferioris_. The curve so formed and the descending limb are covered by the _M. depressor maxillae inferioris_. The artery then passes backwards to form a rich anastomosis in the skin almost as far as the posterior end of the trunk. It supplies the following branches:--

(1) The _Ramus dorsalis_ (Virchow) arises immediately in front of the curve of the main artery; it ascends behind the _M. temporalis_, and passes along the anterior border of the _M. depressor maxillae_ to the skin, where it curves backwards. It supplies small twigs forwards as far as the eyelids.

(2) The _Ramus auricularis_ (Virchow) also arises in front of the curve in the cutaneous artery; sometimes it arises from the _Ramus dorsalis_. The artery winds around the _M. petrohyoideus III_ near its insertion, and so reaches the posterior wall of the tympanic cavity, where it anastomoses with the _R. auricularis_ of the _Ramus maxillaris communis_.]

(3) The _Arteria pharyngo-maxillaris_ (Fig. 148 _p.m._) is a small branch running forwards and outwards to supply the mucous membrane of the larynx, Eustachian tubes, gums, the lower jaw, and the skin under the mouth. It forms a rich anastomosis with branches of the _Ramus maxillaris inferior_ of the occipital artery, and with others from the pharyngeal branch of the carotid artery; a large branch passes forwards to supply the skin of the throat and floor of the mouth.

(4) The _Arteria cutanea pectoris_ (Fig. 149 _c.p._) is distributed to the skin of the breast.

*4.* The *subclavian artery* (_Arteria subclavia_), (Fig. 150 _s_). The subclavian artery arises from the systemic arch immediately behind the occipito-vertebral artery at the level of the second or third vertebra. The artery then runs outwards alongside and in front of the brachial nerve, between the _M. subscapularis_ and the _M. triceps_ to the arm, where it is known as the brachial artery; in its course it gives off:--

*a.* The _Arteria costo-cervicalis_ (Fig. 150, 1). This artery arises near the systemic arch, and runs backwards, parallel to the vertebral column, over the brachial nerve, and across the transverse processes of the vertebrae. It is distributed more especially to the _M. obliquus internus_.

*b.* The _Arteria coraco-clavicularis_ (Fig. 150, 2) arises more externally than the last artery; it accompanies the coraco-clavicular nerve on the dorsal surface of the ventral portion of the shoulder-girdle, and passes between the _M. deltoideus_ and _M. subscapularis_ into the _Foramen ovale_, where it divides to supply these muscles and the _M. pectoralis_.

[Illustration: Fig. 150.

Subclavian artery of the left side.

_A_ Systemic arch. _A_′ Dorsal aorta. _c_ Arteria cutanea medialis superior. _c_′ Arteria cutanea medialis inferior. _ls_ M. levator scapulae. _o.v_ Occipito-vertebral artery. _p_ Arteria pectoralis. _R_ Radial artery _s_ Subclavian artery. _U_ Ulnar artery. 1 Arteria costo-cervicalis. 2 Arteria coraco-clavicularis. 3 Arteria scapularis posterior. 4 Arteria scapularis superior. 5 Cutaneous artery. 6 Arteria subscapularis. ]

*c.* The _Art. scapularis posterior_ (Fig. 150, 3), a small branch arising opposite at the tip of the second transverse process and passing backwards over the _MM. transverso-scapulares_, to which it is distributed.

[Illustration: Fig. 151.

Arteries of the palmar surface of the hand.

_B_ Ulnar artery. _ci_ R. cutaneus medialis inferior. _d_ Digital branches. _F_ M. flexor digitorum communis. _II_ Thumb. _V_ Fifth finger. ]

[Illustration: Fig. 152.

Arteries of the dorsal surface of the hand.

_B_ Ulnar artery. _cri_ R. cutan. rad. inferior. _R_ Radial artery. _II_ Thumb. _V_ Fifth finger. ]

*d.* The _Art. scapularis superior_ (Fig. 150, 4) accompanies several nerves between the _M. subscapularis_, _M. transverso-scapularis major_, and the long head of the _M. triceps_ towards the dorsal surface, where it is distributed to the _MM. infraspinatus_, _latissimus dorsi_, etc.

*e.* The _Ramus cutaneus maxillaris_.

*f.* The _Art. subscapularis_ (Fig. 150, 6) is distributed in the subscapular muscle.

A. The *brachial artery* (_Arteria brachialis_), (Fig. 150) accompanies the brachial nerve under cover of the long head of the _M. triceps_ and over its inner head to the _Plica cubiti_, into which it sinks near the tendon of the _M. sternoradialis_; beyond this point it is continued as the ulnar artery. In its course the brachial artery gives off:--

*a.* The _Arteria pectoralis_ (Fig. 150 _p_).

*b.* The _Arteria cutanea medialis superior_ (Fig. 150 _c_).

*c.* The *radial artery* (_Arteria radialis_), (Fig. 150 _R_) which winds round the humerus with the radial nerve between the muscles of the outer side of the forearm, to which it gives branches: in the palm of the hand it passes between the _M. extensor carpi ulnaris_ and the _M. flexor antibrachii_ to the dorsal surface of the hand, where it anastomoses with the ulnar artery. In its course it supplies:--

(1) Muscular branches to the surrounding muscles.

(2) The _Ram. cut. radialis inferior_, which arises from the radial artery towards the distal end of the forearm, and passes underneath the _M. flexor carpi ulnaris_ to the skin.

B. The *ulnar artery* (_Arteria ulnaris_), (Figs. 150 _U_, 151 _B_) accompanies the ulnar nerve towards the hand, passes between the _M. flexor digitorum communis_ and the _M. anconeus_ to the palm of the hand, and then winds round the outer side to the dorsal surface of the carpus to form its terminal branches. The branches are:--

(1) The _Ram. cutan. med. inferior_ (Fig. 151 _ci_); it arises near the wrist-joint and supplies (α) twigs to the skin of the inner surface; (β) a branch downwards, which courses along the inner side of the second finger to its tip; and (γ) a branch which passes upwards to anastomose with the _R. cutaneus medialis superior_.

(2) In the palm of the hand a branch (Fig. 151 _d_) is given off, which divides to form _Arteriae digitales volares_: one for the second finger, two for the third finger, two for the fourth finger, and one for the fifth finger.

(3) Given off on the dorsum of the hand (Fig. 152) it supplies branches corresponding exactly with those of the palmar surface.

*5.* The *dorsal aorta* (_Aorta communis s. abdominalis_) (Fig. 153 _A_). The two systemic arches unite at about the level of the sixth vertebra to form the dorsal aorta: as already mentioned the union is very incomplete, the dorsal aorta being practically a continuation of the right systemic arch, and only communicating with the left by means of a small opening. The branches are as follows:--

*a.* The *coeliaco-mesenteric artery* (_Arteria intestinalis communis_), (Fig. 153), the true continuation of the left systemic arch, at once divides to form the gastric and mesenteric arteries.

(1) The *gastric artery* (_Arteria gastrica s. coeliaca_) (_c_) immediately divides into two branches:--

α. The _Ramus dexter s. anterior_; this artery gives off the _Arteria hepatica_ to the liver and gall-bladder and passes to the right (anterior) surface of the stomach, running along the attachment of the mesentery and supplying branches forwards to the oesophagus and backwards towards the intestine.

β. The _Ramus sinister s. posterior_ passes to the left (posterior) surface and behaves like the _Ram. dexter_.

(2) The *mesenteric artery* (_Arteria mesenterica superior_ and _inferior_, and the _Arteria splenica_), (Fig. 153 _m_) supplies:--

α. The superior mesenteric artery, which supplies the upper part of the intestine, and gives off a recurrent branch to the stomach, which anastomoses with the gastric arteries.

[Illustration: Fig. 153.

Arterial system of _Rana esculenta_.

_A_ Dorsal aorta. _Ad_ Right systemic arch. _As_ Left systemic arch. _c_ (opposite fore-limb) Carotid artery. _c_ (in abdomen) Coeliac artery. _cm_ Cutaneous artery. _e_ Lingual artery. _H_ Heart. _H_′ Harderian gland. _L_ Liver. _Lu_ Lung. _m_ Mesenteric artery. _M_ Stomach. _M_′ Spleen. _o_ Ophthalmic artery. _p_ Pharyngeal artery. _p_′ Anterior palatine artery. _S_ Subclavian artery. _I_ Carotid arch. _II_ Systemic arch. _III_ Pulmo-cutaneous arch. ]

β. The splenic artery to the spleen.

γ. The inferior mesenteric artery to the lower part of the intestine.

All the arteries to the intestine course in lymph-spaces.

*b.* The *urinogenital arteries* (_Arteriae urino-genitales_), (Fig. 154 _ug_) are four to six small arteries arising from the ventral surface of the aorta between the kidneys: they immediately divide into right and left branches to supply the kidneys, fat-bodies, reproductive organs, and their ducts (see kidney).

*c.* The *lumbar arteries* (_Arteriae lumbales_), are small paired vessels to the neighbouring muscles, and send branches through the intervertebral foramina to the vertebral canal. Sometimes these arteries arise from the _Art. spinalis_ or _Art. vertebralis_, etc.; in the former case they pass outwards from the vertebral canal to the surrounding structures.

*d.* The *haemorrhoidal artery* (_Art. mesenterica inf. s Art. haemorrhoidalis superior_) is a small median artery running from the posterior end of the aorta to the large intestine.

*6.* *Bifurcation of the aorta.* *The iliac arteries* (_Arteriae iliacae communes_). Opposite the middle of the urostyle the aorta bifurcates to form the iliac arteries; each of these courses on the corresponding sciatic plexus to the thigh, beyond which it is continued as the sciatic artery. The branches of the iliac artery are:--

*a.* The *vesico-epigastric artery* (_Arteria epigastrico-vesicalis_), (Fig. 155 _ev_); it arises near the bifurcation, passes outwards on the plexus, and divides into two branches:--

(1) The epigastric artery (_Arteria epigastrica_) (_e_) immediately gives off a recurrent branch to the iliac bone and the _M. ilio-coccygeus_; it then continues to the ventral muscles of the abdominal wall, where it runs forwards on the deeper surface of the _M. obliquus internus_, and is distributed more especially to this muscle.

[Illustration: Fig. 154.

The urinogenital arteries.

_A_ Dorsal aorta. _H_ Testis. _N_ Kidney. _ug_ Urinogenital arteries. ]

(2) The hypogastric artery (_Arteria vesicalis_) (_v_) winds downwards around the sciatic plexus to reach the mesentery, along which it courses to the bladder, where it forms a rich anastomosis.

*b.* The *femoral artery* (_Arteria femoralis s. cruralis_), (Fig. 155 _f_) is the representative of the femoral artery of man, although it does not perform the same functions. The artery passes under the hinder free border of the _M. obliquus internus_ to the thigh, where it lies upon the _M. ilio-psoas_, and sends twigs to the neighbouring muscles, the skin, and lymph-sac (_Lamina inguinalis_), and then divides into:--

(1) A twig, which runs forwards on the ventral surface of the iliac bone and is covered by the epigastric artery.

(2) A twig, running forwards and downwards on the _MM. ilio-psoas_, _vastus internus_, and _sartorius_, to send branches to the hip-joint.

*c.* The *spermatic artery* (_Arteria spermatica_), which arises, in males, from the iliac artery, and ascends to the _Vesicula seminalis_.

[Illustration: Fig. 155.

Bifurcation of the aorta and the iliac arteries.

_e_ Epigastric artery. _ev_ Vesico-epigastric artery. _f_ Femoral artery. _o_ Internal oblique muscle. _v_ Vesical artery. ]

*7.* *Arteries of the hinder extremity.*

A. The *sciatic artery* (_Arteria ischiadica_), (Fig. 156 _i_) is the continuation of the iliac artery; it leaves the pelvis between the hinder (outer) border of the _M. coccygeo-iliacus_ and the inner surface of the origin of the _M. ilio-psoas_, then lies between the former muscle and the origin of the _M. vastus externus_. It appears on the thigh between the _M. vastus externus_ (in front) and the _M. pyriformis_ (behind); it is the main arterial trunk for the hinder extremity. The artery courses backwards, lying upon the sciatic nerve and between the _M. biceps_ and the _M. semimembranosus_; in this course it runs in a lymph-space placed in the _Septum femorale superius_ (see page 259). Arrived at the popliteal space the artery bifurcates to form the peroneal and tibial arteries; near the pelvis it gives off two branches (*a*) and (*b*), and in its course along the thigh two branches (*c*) and (*d*).

*a.* The _Art. haemorrhoidalis inferior_ (_h_) runs backwards and inwards under the _M. pyriformis_ to be distributed in the _M. sphincter ani_ and the skin of the anus.

*b.* The _Art. cutanea femoris posterior v. superior_ (_cf_′) runs with the corresponding nerve and the _M. pyriformis_, and over the _M. semimembranosus_ to the skin of the inner and hinder surfaces of the thigh.

*c.* The _Rami musculares_ supply the _M. semimembranosus_, the _M. biceps_, and the _MM. extensores auris_; the branch to the _M. rectus inferior major_ pierces the muscle in company with the nerve, and is continued as:--

*d.* The _Art. cutanea femoris media_ (_cf_″) to the skin of the middle of the inner surface of the thigh. Several small twigs pierce the _M. rectus internus minor_, reach the skin, and communicate with this artery.

[Illustration: Fig. 156.

Arteries of the hinder extremity.

_cc_ Art. cutanea calcanei. _cf_ Cutaneous branch of the femoral artery. _cf_′ Art. cutanea fem. post. superior. _cf_″ Art. cutanea femoris media. _cgl_ Art cut. genu lateralis superior. _cgl_′ Art. circumflexa genu lateralis inferior. _cgm_ Art. circumflexa genu superior medialis. _cgm_′ Art. circumflexa genu inferior medialis. _ci_ M. coccygeo-iliacus. _g_ M. gastrocnemius. _gl_ M. glutaeus. _h_ Art. haemorrhoidalis inferior. _i_ Sciatic artery. _ml_ Art. malleolaris lateralis. _mm_ Art. malleolaris medialis. _p_ Art. peronea. _p_′ Muscular branch to the M. peroneus. _P_ M. pyramidalis. _ra_ M. rectus anterior. _ri_″ M. rectus internus. _sm_ M. semimembranosus. _su_ Art. suralis. _t_ Tibial artery. _to_ Aperture in tibio-fibula. _tr_ Art. tarsea. _ve_ M. vastus externus. ]

B. The *peroneal artery* (_Art. peronea_), (Fig. 156 _p_) runs outwards under cover of the tendon of the _M. biceps femoris_, and accompanies the peroneal nerve downwards to give off:--

*a.* The _Art. circumflexa genu lateralis superior_, which runs forwards on the outer side of the knee, gives a twig to the joint, and is continued as:--

*b.* The _Art. cutanea genu lateralis superior_ (_cgl_) to the skin of the anterior and outer sides of the knee. It anastomoses with branches of the _Arteriae circumflexae genu mediales_ to form a rich anastomosis (_Rete articulare genu_): other branches pass upwards to inosculate with the _Art. cutanea femoris anterior_ (_cf_), and others downwards to anastomose with the next artery.

*c.* The _Art. circumflexa genu lateralis inferior_ (_cgl_′) runs under the tendon of origin of the gastrocnemius to the outer side of the knee, and terminates in the skin as the _Art. cutanea genu lateralis inferior_. Some of the cutaneous twigs pass upwards to anastomose with the _Art. cut. genu lat. superior_, others downwards to anastomose with the _AA. malleolares_.

*d.* A muscular branch (_p_′) for the _M. peroneus_; it is the real continuation of the peroneal artery, and runs behind the outer tendon of origin of the gastrocnemius to be distributed in the _M. peroneus_.

C. The *tibial artery* (_Arteria tibialis_), (Fig. 156 _t_), arises at the bifurcation of the sciatic, and runs inwards, meeting the tibial nerve between the tendons of origin of the _M. gastrocnemius_, and deep in the popliteal space under cover of the calf-muscles. It then pierces the _M. tibialis posticus_, and leaves this to perforate the tibio-fibula (see p. 50), appearing again on the anterior surface as the anterior tibial artery. Before meeting the tibial nerve this artery gives off the following branches:--

*a.* The _Art. circumflexa genu superior medialis_ (_cgm_), which winds round to the front of the knee-joint, and gives off a cutaneous branch, the _Art. cutanea genu medialis superior_, which is distributed in the skin of the inner side of the knee and anastomoses above with the _Art. cutanea femoris media_, below with the following branches (*b*, *c*, and *d*).

*b.* The _Art. circumflexa genu inferior medialis_ (_cgm_′) supplies twigs to the knee-joint, and passes to the skin of the knee and inner surface of the calf as the _Art. cutanea inferior medialis_.

*c.* Muscular twigs to the _M. gastrocnemius_.

*d.* The _Art. suralis_ (_su_); this accompanies the _N. suralis_ downwards along the calf-muscle, and is distributed in the skin of the inner side of the heel.

*e.* While passing between the fibres of the _M. tibialis posticus_, the tibial artery gives off muscular twigs; one larger than the rest is known as the _Ramus descendens_.

D. The *anterior tibial artery* (_Arteria tibialis antica_), (Fig. 157 _t.a._) is the continuation of the tibial artery after piercing the tibio-fibula. It runs downwards on the anterior surface of the leg, then between the two heads of the _M. tibialis anticus_ to the dorsum of the foot, where it is continued as the _Arteria dorsalis pedis_. It supplies:--

[Illustration: Fig. 157.

Arteries of the dorsal surface of the foot.

_c.c._ Art. cutanea calcanei. _c.c.i._ Art. cutanea cruris inferior. _Ft_′ M. flexor tarsi. _h_ Art. cutanea hallucis. _i1_ Art. interossea dorsalis I. _i2_ Art. interossea dorsalis II. _i3_ Art. interossea dorsalis III. _i4_ Art. interossea dorsalis IV. _ml_ Art. malleolaris lateralis. _m.m._ Art. malleolaris medialis. _t.a._ Anterior tibial artery. _ta_* Bifurcation of the dorsalis pedis artery. _tr_ Art. tarsea. ]

*a.* _Rami musculares_ to the _M. peroneus_, _M. extensor cruris_, and to the _M. flexor tarsi anterior_.

*b.* The _Art. cutanea cruris inferior_ (_c.c.i._) passes between the two heads of the _M. tibialis anticus_ to the skin of the anterior and outer sides of the leg.

*c.* The _Art. cutanea calcanei_ (_c.c._) is given off at the ankle-joint; it runs outwards on the lower end of the tibio-fibula, giving branches to the joint, then backwards between the tibio-fibula and the _M. peroneus_ to be distributed to the skin of the heel. Above it anastomoses with the _A. circumflexa genu inf. lateralis_, and below with the malleolar arteries.

*d.* The _Art. malleolaris lateralis_ (_ml_) arises a little beyond the last artery; it runs outwards under the origin of the _M. flexor tarsi_, gives branches to the joint and muscles, and terminates in the skin of the outer border and dorsal surface of the foot.

*e.* The _Art. malleolaris medialis_ (_m.m._) arises at about the same level as the _Art. malleolaris lat._ from the inner border of the anterior tibial artery. It supplies branches to the joint, gives numerous branches to the skin, which anastomose with the _Art. suralis_, and passes to the inner border of the foot, where it ends by distributing branches to the _M. plantaris_, the extensor aponeurosis, and, as the _Art. cutanea plantaris_, to the skin of the sole of the foot.

E. The *dorsal artery* of the foot (_Art. dorsalis pedis_), (Fig. 157 _t.a._) runs under the _M. flexor tarsi posterior_ to the point _ta_*, where it is superficial; the artery then bifurcates; the branches are:--

[Illustration: Fig. 158.

Arteries of the sole of the foot.

_i_ Art. interossea. _pf_ Rami perforantes. ]

*a.* The _Art. tarsea_ (_tr_) which arises from the dorsal artery of the foot while under cover of the _M. flexor tarsi posterior_; it passes to the _M. extensor digiti V_ and to the skin of the dorsum and outer border of the foot. One branch courses along the outer border of the fifth toe to its tip; another passes upwards to anastomose with the neighbouring vessels.

*b.* The inner branch, formed by the bifurcation of the dorsal artery of the foot, at once divides to form:--

(1) The _Art. cutanea hallucis_ (_h_) to the supplemental great toe.

(2) The _Art. interossea dorsalis I_ (_i^1_), which at once bifurcates to form two _Rami digitales_ for the first and second toes; these inosculate with the _Art. cutanea plantaris_, and send twigs to the skin of the inner border of the foot.

*c.* The outer branch formed by the bifurcation of the dorsal artery divides to form the _Arteriae interossei dorsales II_, _III_, and _IV_ (_i^2_, _i^3_, _i^4_); they are distributed in a rich anastomosis to the web.

*d.* The _Arteria interossea_ (Fig. 158 _i_) arises from the dorsal artery of the foot at the tarsus, and perforates the membrane between the astragalus and calcaneum to reach the sole of the foot. It forms a rich subcutaneous plexus on the calcar, and anastomoses with the _Rami perforantes_ (Fig. 158 _pf_), which pass above the upper borders of the _Musculi interossei_ to reach the plantar surface, where they give off small _Rami interossei volares_ to anastomose with the _AA. interosseae dorsales_.

III. THE VEINS.

(The arrangement of this section has been modified.)

The blood, distributed to the body by means of the arteries, is returned to the heart by the veins, which conduct the blood directly or indirectly to the auricles. The pulmonary vein opens directly into the left ventricle, the three _Venae cavae_ open into the _Sinus venosus_.

A. *Vein opening into the left auricle.*

The *pulmonary vein* (_Vena pulmonalis communis_), (Fig. 159 _vp_). The blood returning from each lung is gathered into a vessel lying along the inner side of the root of the lung. That of the right side is somewhat longer than the left; the two vessels (_Venae pulmonales dextra et sinistra_) run above the corresponding anterior caval veins to form a common trunk, the pulmonary vein, which opens into the left auricle (see p. 215).

B. *Veins opening into the* _Sinus venosus_.

The veins opening into the _Sinus venosus_ are the three caval veins; of these the two anterior open into the anterior angles of the _Sinus venosus_, the posterior into the posterior angle.

*1.* The *Anterior Caval Veins* (_Vena cava superior_), (Figs. 133 _V_, 159 _C a_) are a pair of large veins opening into the _Sinus venosus_ and returning to it blood from the fore-limbs and sides of the head. Each vein is formed by the union of a small vein, the external jugular, with two large veins, the innominate and the subclavian veins.

*a.* The *external jugular vein* (_Vena jugularis externa_), (Fig. 159 _je_) is formed, at the outer border of the hyoid bone, by the union of two veins:--

(1) The lingual vein (_Vena lingualis_) (Fig. 161 _l_). This originates at the tip of the tongue and passes in a very tortuous course along the ventral surface of the hyoid; it receives numerous branches from the tongue and hyoid muscles.

(2) The mandibular vein (_Vena maxillaris inferior_), (Fig. 161 _m_) runs along the insertion of the _M. submaxillaris_, and turns inwards at its hinder border to join the lingual vein.

*b.* The *innominate vein* (_Vena anonyma_), (Fig. 160 _A_) is formed by the union of the internal jugular and the subscapular veins. By tracing the innominate vein upwards between the suspensorium and the shoulder-girdle, the internal jugular vein will be seen to receive the vertebral vein at the outer border of the _M. levator scapulae_. The left innominate vein receives the _Vena bulbi anterior_ from the _Truncus arteriosus_ (p. 222).

[Illustration: Fig. 159.

Schema of the veins of _Rana esculenta_.

_a_ Subclavian vein. _ab_ Anterior abdominal vein. _Ad_ Right auricle. _As_ Left auricle. _Ca_ Anterior vena cava. _Cp_ Posterior vena cava. _cm_ Cutaneous vein. _d_ Vena dorso-lumbalis. _D_ Intestine. _f_ Femoral vein. _i_ Sciatic vein. _ic_ Vena communicans iliaca. _je_ External jugular vein formed by lingual and maxillary veins _l_ and _m_. _ji_ Internal jugular vein. _L_ Hepatic veins. _N_ Kidney. _o_ Oviducal veins. _P_ Hepatic portal vein. _raI_ Renal portal vein. _raII_ Secondary renal portal veins. _re_ Renal veins. _s_ Subscapular vein. _SC_ Sinus venosus. _va_ Innominate vein. _vc_ Vena bulbi posterior (cardiac vein). _vp_ Pulmonary veins. ]

(1) The *internal jugular vein* (_Vena jugularis_), (Fig. 160 _J_) can be traced from the border of the _M. levator scapulae_ upwards and forwards to the hinder part of the prootic bone: it then passes forwards under the lateral process of the prootic, in a groove on the anterior surface of the same bone, towards the hinder angle of the orbit, where it receives the veins from the cranial cavity (see vessels of brain, p. 165), and also a branch from the orbit.

[Illustration: Fig. 160.

Distribution of the internal jugular vein and the anterior portion of the cutaneous vein.

_A_ Innominate vein. _c.m._ Cutaneous vein. _f_ Nasal vein. _h_ Harderian gland. _H_ Skin, reflected downwards. _J_ Internal jugular vein. _L_ Anterior lymph-heart. _l_ M. levator scapulae. _O_ M. obliquus internus. _o_ Vena orbitalis anterior. _o_′ Vena orbitalis posterior. _P_ Lateral process of the prootic bone. _S_ Subscapular vein. _S_′ Shoulder-girdle. _T_ Tympanic membrane. _V_ Vertebral vein. _2_ Transverse process of the second vertebra. _3_ Transverse process of the third vertebra. _4_ Transverse process of the fourth vertebra. ]

α. [The _Vena orbitalis media_ (Virchow); it arises from the anterior internal angle of the orbit, from the Harderian gland, the nasal cavity, or from other veins on the anterior wall of the orbit. The vessel lies close to the cranium, immediately underneath the _Arteria nasalis_, and sinks under the _M. rectus superior_ to join the internal jugular vein. In its course it receives the _Vena bulbi superior_ (see eye), and near its termination communicates with the _Vena orbitalis posterior_.]

β. The _Vena vertebralis_ (Fig. 160 _V_) arises posteriorly and runs forwards over the transverse processes of the vertebrae, the _Musculi intertransversarii_, and the _M. levat. scapulae_, to join the internal jugular vein. In its course it receives branches (_Venae spinales_) from the vertebral canal through the intervertebral foramina, and cutaneous branches which accompany the corresponding arteries and nerves through the dorsal lymphatic sac. The vein pulsates in consequence of its connection with the anterior lymph-heart (Müller).

(2) The *subscapular vein* (_Vena subscapularis_), (Fig. 160 _S_). This vein arises in the transverse abdominal muscles and the muscles of the shoulder girdle; it unites with the internal jugular vein under the shoulder-girdle.

*c.* The *subclavian vein* (_Vena subclavia_), (Fig. 159) passes backwards from the anterior caval vein on the dorsal surface of the coracoid bone and the clavicle, and then under cover of the _Portio sternalis_ of the _M. pectoralis major_, to the internal border of the _Portio abdominalis_ of the _M. pectoralis major_, where it is formed by the union of the cutaneous vein and the brachial vein.

[Illustration: Fig. 161.

The anterior caval vein and its branches.

_a_ Innominate vein. _c.m._ Cutaneous vein. _c.s._ Anterior cava vein. _i_ Internal jugular vein. _i_′ External jugular vein. _l_ Lingual vein. _m_ Mandibular vein. _s_ Brachial vein. _s.c._ Subscapular vein. ]

(1) The cutaneous vein (_Vena cutanea magna_, Ecker; _Vena musculo-cutanea_, Gruby), (Figs. 160, 161, and 162 _c.m._). This vein arises by small branches in the head; these are:--

α. The _Vena nasalis_ (Virchow); it arises by an upper and a lower branch from around the nostril, and courses backwards along the superior maxillary bone to about the middle of the orbit, where it joins the facial vein.

β. The _Vena orbitalis anterior_ (Virchow), (_Vena ophthalmica anterior_, Ecker), (Fig. 160 _o_) commences at the Harderian gland from a rich anastomosis, receives branches from the floor and anterior wall of the orbit, and joins the facial vein with the _Vena nasalis_.

[Illustration: Fig. 162.

Course of the cutaneous vein as seen from the side.

_c.m._ Cutaneous vein. _d_ M. depressor maxillae. _i_ M. infraspinatus. ]

γ. The _Vena orbitalis posterior_ (Virchow), (_Vena ophthalmica posterior_, Ecker), (Fig. 160 _o_′) arises on the posterior wall of the orbit on the _M. pterygoideus_; it passes under the _Processus zygomaticus_ to join the facial vein, and in its course receives the _Vena ophthalmica_ (see eye), and communicates with the _Vena orbitalis medialis_ and the internal jugular vein.

δ. The _Vena facialis_ (Fig. 160) is formed about the middle of the orbit by the union of the _Vena nasalis_ and the _Vena orbitalis anterior_; it courses backwards towards the angle of the jaw. On reaching the _M. depressor maxillae_, about 4 mm. in front of the angle of the jaw, it passes on to the skin. It receives in its course the _Venae palpebrales_ (Fig. 162) and the _Vena orbitalis posterior_.

The musculo-cutaneous vein is the direct continuation of the _Vena facialis_ after this has left the upper jaw; it immediately receives one or more twigs (_Venae tympanicae_), (Fig. 162) from the tympanic membrane and the tympanic cavity.

The vein then courses backwards in the outer wall of the lateral lymph-sac as far as the middle of the trunk, where it passes, by means of the _Septum abdominale_, to the outer border of the _Portio abdominalis_ of the _M. pectoralis_; here the vein curves round to pass forwards between the fibres of this muscle to its inner border where it terminates by joining the brachial vein. In the whole of this lengthy course the vein receives numerous branches from the neighbouring parts.

[Illustration: Fig. 163.

Veins in the region of the kidney.

_a_ Renal portal vein. _a_′ Dorso-lumbar veins. _abd_ Anterior abdominal vein. _d_ Intestine. _f_ Femoral vein. _i_ Sciatic vein. _N_ Kidney. _o_ Right ovary, drawn to the left. _o_′ Oviduct. _ov_ Oviducal veins. _p_ Mesenteric veins. _r_ Renal veins. _V_ Bladder. _v.c.i._ Posterior vena cava. _Vv_ Vesical veins. ]

(2) The *brachial vein* (_Vena brachialis_) is formed in the _Plica cubiti_ by the union of two veins.

α. The *radial vein* (_Vena radialis_) arises on the dorsum of the hand from a venous arch, the distal convexity of which receives the _Venae digitales dorsales_: the vein courses superficially along the outer side of the forearm to the elbow.

β. The *ulnar vein* (_Vena ulnaris_) arises from the veins in the palm of the hand, and courses towards the elbow, lying deeply between the muscles of the inner and outer surfaces of the forearm. In the elbow the vein becomes superficial near the tendon of the _M. sterno-cleidoradialis_, and joins the radial vein to form the brachial vein.

The cutaneous veins of the fore-limb follow courses corresponding with those of the arteries.

*2.* The *Posterior Caval Vein* (_Vena cava inferior_), (Fig. 159 _Cp_, 163 _v.c.i._). The posterior caval vein is a median vein which, commencing between the kidneys, runs forwards to open into the posterior end of the _Sinus venosus_. It receives the hepatic, renal, and ovarian or spermatic veins.

*a.* The hepatic veins (_Venae hepaticae_), (Fig. 164 _v.h._) are two in number, one from either side of the liver; they open into the posterior caval vein near the _Sinus venosus_.

*b.* The *renal veins* (_Venae renales_ or _Venae revehentes_), (Fig. 163 _r_) are four or five small vessels on each side; they pass from the inner border of the kidney inwards and forwards, to form, by their union, the posterior caval vein. The most anterior receive branches from the fat-bodies (see kidney).

*c.* The *spermatic* or *ovarian veins* are four or five in number on each side; they open into the posterior caval vein between the renal veins.

*3.* The *Portal Systems*.

[There are, in the frog, two portal systems; the renal and the hepatic. Each of these receives vessels which are derived, directly or indirectly, from the veins of the hinder extremity.

The femoral vein on entering the pelvis divides to form two branches; an iliac vein placed dorsally, and a pelvic vein placed ventrally; the two pelvic veins converge to the middle line of ventral wall of the abdomen, where they unite to form the anterior abdominal vein.]

*a.* The *renal portal vein* (_Vena renalis advehens princeps_), (Fig. 163 _a_). This vein is formed by the union of the sciatic and the iliac veins; it courses forwards to the outer border of the kidney, and is distributed, by numerous branches, to that organ, chiefly on its dorsal surface. It receives the following veins:--

(1) The *iliac vein* (_Vena iliaca externa_); this is the dorsal branch formed by the bifurcation of the femoral vein.

(2) The *sciatic vein* (_Vena ischiadica_), (Figs. 163 and 165 _i_) arises at the popliteal space, courses upwards in company with the sciatic nerve between the _M. semitendinosus_ and the _M. biceps_, then passes, still with the nerve, between the _M. vastus externus_ and the _M. pyramidalis_ into the pelvis. It continues forwards to join the iliac vein. At the root of the thigh this vein communicates with the femoral vein by the _Ramus communicans iliacus_.

(3) The *dorso-lumbar vein* (_Vena dorso-lumbalis_), (Fig. 163 _a_′) is a vein (or more usually several) arising by twigs in the dorsal and outer walls of the abdomen; it joins the renal portal vein opposite the kidney.

(4) The *oviducal veins* (Fig. 163 _ov_) are irregular veins from the oviducts, which open either into the dorso-lumbar vein, or into the renal portal vein.

*b.* The *hepatic portal system*.

The liver receives blood from two sources: (1) from the hind-limbs by means of the anterior abdominal vein, and (2) from the alimentary canal by the hepatic portal vein.

[Illustration: Fig. 164.

Veins of the liver.

_AA_ Auricles. _aa_ Right and left branches of anterior abdominal vein. _b_ Ramus descendens. _c_ Vena bulbi (Vena cardiaca). _D_ Intestine. _G_ Gall-bladder. _L.l._ Left lobe of liver. _L.r._ Right lobe of liver. _P_ Hepatic portal vein. _P_′ Intestinal veins. _P_″ Gastric veins. _S_ Sinus venosus. _V_ Ventricle. _Va_ Anterior abdominal vein. _V.c.i._ Posterior vena cava. _v.h._ Hepatic veins. ]

The *anterior abdominal vein* (_Vena abdominalis_), (Figs. 159 _ab_, 164 _Va_) is formed, a little in front of the symphysis pubis, by the union of the two pelvic veins. It courses forwards along the middle line of the ventral body-wall until opposite the liver, where it ascends and divides into three branches, of which two enter the right and left lobes of the liver respectively. The third, the _Ramus descendens_, joins the hepatic portal vein. The anterior abdominal vein receives the following veins:--

α. The vesical vein (_Vena vesicalis_), (Fig. 163 _Vv_); a median vein arising in the groove between the lobes of the bladder from lateral branches, which extend outwards on the bladder. This vein communicates above with other vesical twigs which open into the haemorrhoidal vein.

β. Parietal veins, which join the anterior abdominal vein in its course along the ventral body-wall.

γ. A cardiac vein (_Vena cardiaca_), (Figs. 142, 159 _vc_, 164 _c_), which joins the anterior abdominal vein just before its division (see p. 222).

The *hepatic portal vein* (_Vena portarum_), (Figs. 159, 164 _P_) is formed by the union of the gastric, intestinal, splenic, and one of the haemorrhoidal veins. The large vein so constituted passes forwards towards the liver, receives the _Ramus descendens_ from the anterior abdominal vein, and then passes into the left lobe of the liver. Its branches are the following:--

(1) The *gastric veins*. The stomach has three veins:--

α. [The _Vena coronaria ventriculi_, which receives blood from the hinder end of the oesophagus and anterior portion of the stomach.

β and γ. Two other veins which form an _Arcus coronarius_ on the concave surface of the stomach; the hinder receiving in addition the small _Venae pancreaticae_ and the _Vena duodenalis_; the trunk so formed receives the _Vena coronaria ventriculi_ (Hoffmann).

(2) The *intestinal veins*; the veins of that portion of the alimentary canal between the middle of the duodenum and the anterior end of the large intestine open into a common vein which joins the hepatic portal vein.

(3) The *splenic vein* joins either the hepatic portal vein or one of the intestinal veins.

(4) The *haemorrhoidal veins* are three in number; the anterior opens into the splenic vein, the remaining two into the portal veins through the agency of the intestinal veins.]

*4.* *The Veins of the Hinder Extremity.*

The hinder extremity has two venous trunks, the sciatic vein and the femoral vein.

*a.* The *femoral vein* (_Vena femoralis_), (Fig. 165 _f_) is the larger venous trunk of the hinder extremity. It arises in the popliteal space as a direct continuation of the posterior tibial vein, courses upwards in company with the sciatic artery and nerve, then leaves these to wind forwards and outwards, and appears between the origins of the _M. vastus externus_ and of the _M. rectus anterior_. The vein here gives off the _Ramus communicans iliacus_ to the sciatic vein, and turns forwards and downwards around the _M. glutaeus maximus_ to reach the floor of the pelvis, near the femoral artery. The vein then bifurcates to form the pelvic and iliac veins.

[Illustration: Fig. 165.

Veins of the hinder extremity, half schematic.

_c.i._ Vena communicans iliaca. _f_ Femoral vein. _i_ Sciatic vein. _i_′ Vena cutanea cruris medialis. _r.a._ M. rectus anterior. _s.m._ M. semimembranosus. _v.e._ M. vastus externus. ]

(1) The _Ramus communicans iliacus_ (Fig. 165 _c.i._) forms a communication with the sciatic at the base of the thigh.

(2) The posterior tibial vein (_Vena tibialis postica_), of which the femoral is a continuation, arises on the dorsal surface of the toes and foot. It runs superficially on the _M. extensor longus digiti primi_ over the ankle-joint, courses upwards and winds round the outer surface of the tibio-fibula to the flexor surface. It receives, in its course, muscular branches, and at the knee a large cutaneous branch.

*b.* The *sciatic vein*: this vein has already been described (see p. 247), but the vein from which it arises requires description.

The *anterior tibial* vein (_Vena tibialis antica_) arises on the dorsum of the foot by twigs from the toes; it courses under the _M. extensor longus digiti primi_, then upwards on the anterior surface of the leg, and enters the canal in the tibio-fibula to appear on its hinder surface. The vein then receives twigs from the _M. peroneus_, the _M. tibialis posticus_, the _M. gastrocnemius_, and a large cutaneous branch.

α. The _Vena cutanea cruris medialis_ (Fig. 165 _i_′) receives branches from both above and below, and enters the popliteal space to join the anterior tibial vein.

β. The anastomosis on the dorsum of the foot, from which the anterior tibial vein arises, receives perforating twigs from the plantar surface.