PART II.

THE LYMPHATIC SYSTEM.

(The arrangement of this section has been considerably altered.)

[The lymphatic system of the frog may, for descriptive purposes, be advantageously treated of in four parts:

*1.* The subcutaneous lymph-sacs.

*2.* The lymph-hearts.

*3.* The lymph-spaces of the body, and those lying between the various organs.

*4.* The lymph-vessels of the separate organs.

The first two parts will be described in this section; the remainder with the organs or parts of the body with which they are more intimately associated. The spleen will be described with the abdominal viscera.

*1.* The Subcutaneous Lymph-Sacs.

A number of large spaces exist between the skin and the muscles, in which there is no direct attachment between these parts. These spaces are separated from each other by thin connective-tissue septa, stretched between the muscles and the skin, and by attachments of the skin to the underlying structures.

Joh. Müller first demonstrated that these spaces were connected with the lymphatic system, and that the contained fluid was lymph. Although this fact was contradicted by Meyer it received confirmation from Stannius, Leydig, and especially from Recklinghausen, who showed that the fluid of the lymph-sacs was carried away by the lymphatics, and that later it entered the blood-stream.

A. The Lymph-sacs of the Head and Trunk.

*a.* The *septa*. The connective-tissue septa themselves contain sinuses which occupy the space between their two surfaces (Fig. 166) these septal sinuses receive the contents of the cutaneous lymph-vessels and forward their contents into lymph-vessels situated in the septa. Such a sinus is shown in transverse section in Fig. 166 which is a section of the ventral septum. The same sinus, in plan, is seen in Fig. 167.

(1) The *dorsal septum* (_Septum dorsale_), (Figs. 169 and 171 _d_) of each side commences at the tympanic membrane; it is then attached to the _M. depressor maxillae_, _M. infraspinatus_, and _M. longissimus dorsi_; and continued backwards over the _M. obliquus abdominis externus_ to the anterior end of the _M. glutaeus_, whence it extends along the iliac bone, where it is connected with the posterior lymph-heart and the _M. pyriformis_, to the tip of the urostyle. At the tip of the _M. glutaeus_ it is joined by the iliac septum. The posterior part of the septum is horizontal, and forms the roof of the iliac lymph-sac.

[Illustration: Fig. 166.

Transverse section of a septum with the attached skin, its contained sinus injected with blue injection mass.

_H_ Skin. _s_ Septum. _S_ Sinus contained in the septum. ]

[Illustration: Fig. 167.

The _sinus abdominalis lateralis_ (Ecker) injected with blue mass.

_H_ Skin with its lymph-vessels. _S_ Sinus of the septum with lymph-vessels opening into it. _s_ The septum cut parallel with the skin. ]

(2) The *ventral septum* (_Septum abdominale_), (Figs. 169, 170, and 171 _a_), commencing at the _Symphysis pubis_, runs forwards and outwards, on either side, along the outer border of the _M. rectus abdominis_ to the _Portio abdominalis_ of the _M. pectoralis_ (_p_‴), where it is attached, at a right angle, to the pectoral septum; it then extends forwards, after attachment to the axillary septum, to the outer angles of the maxillary septum. At the root of the anterior extremity it divides to enclose the root of the limb, and so form the axillary septum.

(3) The *pectoral septum* (_Septum pectorale_), (Figs. 170 and 171 _p_) is attached to the superficial surface of the _M. pectoralis_ (_Portio sternalis_, _anterior_ and _posterior_); it runs transversely across the body, and is attached at its outer end to the ventral and to the maxillary septa. The septum passes obliquely backwards and downwards to be attached to the skin, and so forms a very acute angle with the _M. cutaneus pectoris_ (_cp_): a vertical band of connective-tissue, broad behind, narrow in front, extends in the middle line from the septum to the body wall; from it a certain amount of loose connective-tissue extends in all directions, and forms open lymph-spaces between the _MM. cutanei pectorales_ and the vertical septum.

(4) The *perineal septum* (_Septum perineale_), (Fig. 170 _pe_). This median septum extends from the attachment of the dorsal septum to the tip of the urostyle, backwards to the symphysis pubis, where it joins the ventral septa. In its attachment it follows the middle line of the perineum.

(5) The *maxillary septum* (_Septum maxillare_), (Figs. 170, 171 _m_) is attached by either extremity to the dorsal septum, near the tympanic membrane, is continued downwards to unite with the anterior end of the ventral septum, and then runs across the anterior pectoral region, forming a curve with the convexity forwards. It has inserted into it fibres of the _M. submaxillaris_. The septum is formed of very loose tissue, and frequently contains deposits of fat; it encloses a well-marked septal sinus, the _Sinus thoracicus transversus_ (Ecker).

[Illustration: Fig. 168.

Sinus thoracicus transversus (Ecker).

_cp_ M. cutaneus pectoralis. _H_ Skin reflected forwards. _s_ Sinus with its afferent vessels. ]

(6) The *iliac septum* (Figs. 169, 172 15, 173 _S_′) is a septum extending from the dorsal septum to the inguinal septum. It is attached to the dorsal septum opposite the anterior end of the _M. glutaeus_, and extends outwards and downwards to the inguinal septum. In it the _M. cutaneus iliacus_ passes from the trunk to the skin.

[Illustration: Fig. 169[64].

The lymph-sacs of _Rana esculenta_, seen from the dorsal surface.

_1_ Dorsal lymph-sac. _3_ Lateral lymph-sac. _7_ Brachio-radial lymph-sac. _9_ Femoral lymph-sac. _10_ Suprafemoral lymph-sac. _11_ Interfemoral lymph-sac. _12_ Crural lymph-sac. _13_ Dorsal lymph-sac of the foot. _14_ Plantar lymph-sac of the foot. _15_ Iliac lymph-sac. _a_ Ventral septum. _d_ Dorsal septum. _f_′ Superior femoral septum. _f_‴ Intermediate femoral septum. _i_ Inguinal septum. _s_ Posterior brachial septum. _s_‴ Anterior brachio-radial septum. _V_ Vocal sac. ]

[Footnote 64: In Figs. 168, 169, and 170 the dotted lines denote the boundaries of the various lymph-sacs.]

(7) The *inguinal septum* (_Lamina inguinalis_, Ecker), (Figs. 169 171), the dotted line near 15, Fig. 172, separates the belly from the thigh; on the ventral surface it is attached to the groove which forms the boundary between the belly and thigh; on the dorsal surface it is more posterior, and is attached to the dorsal surface of the muscles of the thigh at some little distance from the trunk. It completely surrounds the root of the hinder limb. It has attached to it the ventral, dorsal, and iliac septa, together with the septa of the thigh.

*b.* The *lymph-sacs*.

(1) The *dorsal lymph-sac* (_Saccus cranio-dorsalis_), (Figs. 169 and 171 1). This is a large lymph-sac, extending from the tip of the snout to the tip of the urostyle; it is bounded in front by the attachment of the skin to the premaxillary bones; the line of attachment is continued, on either side, along the inner border of the external nares, then forms a pouch towards the jaw and in front of the eye, and runs backwards along the upper border of the orbit, where it is attached to the upper eyelid, to the inner border of the tympanic membrane. In this course the skin is firmly attached to the underlying parts. The lateral boundary of the lymph-sac, behind this point, is formed by the dorsal septum, which separates it from the lateral lymph-sac.

(2) The *ventral lymph-sac* (_Saccus abdominalis_), (Figs. 170, 171 _2_) is triangular in form, with the base forwards at the breast, and the apex behind at the pelvic symphysis; it occupies the space between the skin below and the belly muscles and part of the _M. pectoralis_ above. It is bounded anteriorly by the pectoral septum (_p_) and laterally by the ventral septa (_a_).

(3) The *lateral lymph-sac* (_Saccus lateralis_), (Figs. 169, 170, and 171 3) exists on either side; below, the sac is bounded by the ventral septum (_a_), above by the dorsal septum (_d_), anteriorly by the maxillary septum (_m_), and posteriorly by the inguinal septum (_i_) and the wall of the iliac lymph-sac.

(4) The *submaxillary lymph-sac* (_Saccus submaxillaris_), (Figs. 170 and 171 4) is a space between the _M. submaxillaris_ and the skin; the sac is bounded behind by the maxillary septum, which separates it from the pectoral lymph-sac, and more laterally from the lateral lymph-sac. In front and at the sides the skin is firmly attached to the margin of the mandible.

(5) The *pectoral lymph-sac* (_Saccus thoracicus_), (Figs. 170 and 171 _5_) lies between the submaxillary and ventral lymph-sacs. The sac is bounded behind by the pectoral septum (_p_), and in front by the maxillary septum (_m_).

Illustration: Fig. 170.

Lymph-sacs of _Rana esculenta_, seen from the ventral surface.

_2_ Ventral lymph-sac. _3_ Lateral lymph-sac. _4_ Submaxillary lymph-sac. _5_ Thoracic lymph-sac. _6_ Brachio-ulnar lymph-sac. _8_ Anterior brachial lymph-sac. _9_ Femoral lymph-sac. _11_ Interfemoral lymph-sac. _12_ Crural lymph-sac. _13_ Dorsal lymph-sac of the foot. _14_ Plantar lymph-sac of the foot. _a_ Ventral septum. _a_′ Anterior division of ventral septum. _a_″ Posterior division of ventral septum. _cf_ Intermediate femoral septum. _cp_ M. cutaneus pectoris. _f_″ Inferior femoral septum. _i_ Inguinal septum. _i_′ Attachment of inguinal septum to skin. _m_ Maxillary septum. _m_′ Attachment of maxillary septum to skin. _p_ Pectoral septum. _p_‴ Port. abdom. of the M. pectoralis. _pe_ Perineal septum. _r_ M. rectus abdominis. _ri_″ M. rectus internus minor. _s_″ Anterior brachio-ulnar septum. _s_‴ Anterior brachial-radio septum. _sm_ Musc. submaxillaris. ]

[Illustration: Fig. 171.

The lymph-sacs of _Rana esculenta_, seen from the side.

_1_ Dorsal lymph-sac. _2_ Ventral lymph-sac. _3_ Lateral lymph-sac. _4_ Submaxillary lymph-sac. _5_ Pectoral lymph-sac. _9_ Femoral lymph-sac. _10_ Suprafemoral lymph-sac. _12_ Crural lymph-sac. _15_ Iliac lymph-sac. _a_ Ventral septum. _d_ Dorsal septum. _i_ Inguinal septum. _m_ Maxillary septum. _m_′ Attachment of M. submaxillaris to the skin. _p_ Pectoral septum. _sm_ M. submaxillaris. _v_ Vocal sac. ]

(6) The *iliac lymph-sac* (_Saccus iliacus_), (Figs. 171 and 172 _15_, 173) does not really belong to the subcutaneous lymph-sacs, as it does not lie directly under the skin except by a very narrow border. It is bounded in front by the iliac septum, above by the dorsal septum, and posteriorly by the inguinal septum. By these boundaries a space is enclosed, which lies under the dorsal septum and dorsal sac, and at the same time partly under the lateral sac. In this sac the _M. glutaeus_, the anterior ends of the _M. vastus externus_, _M. rectus anterior_, and _M. cutaneus iliacus_, lie free together with the hindmost part of the _M. obliquus abdominis externus_, and the hinder portion of the posterior lymph-heart. Anteriorly the floor is depressed between the _M. obliquus abdominis_ and the _M. glutaeus_, the depression leading to a canal, which communicates with the abdominal cavity.

B. The Lymph-sacs of the Anterior Extremity.

*a.* The *septa*.

(1) The *axillary septum* (_Septum axillare_), (Figs. 170 _a_′, _a_″, 171) is practically a portion of the ventral septum, which divides at the root of the arm to enclose it. The dorsal and ventral portions of this circular septum have received special names.

α. The dorsal axillary septum (_Septum axillare dorsale_) crosses the _M. triceps_ and joins the pectoral septum.

β. The ventral axillary septum (_Septum axillare dorsale_) passes through the axilla and joins the pectoral septum.

The circular axillary septum has attached to it the following:--

(2) The *posterior brachial septum* (_Septum brachiale posticum_) (Fig. 169 _s_); it is attached along the middle line of the extensor surface of the arm (long head of the _M. triceps_) to the elbow and to the forearm (_MM. anconaei_), then passes obliquely over the volar surface of the hand to the fourth finger.

(3) The *anterior brachio-ulnar septum* (_Septum brachiale anticum ulnare_), (Fig. 170 _s_″) commences at the same point as the foregoing, passes obliquely over the outer head of the _M. triceps_, and is continued over the _M. flexor antibrachii lateralis_, _M. supinator longus_, and _M. extensor digitorum communis_, to the dorsal surface of the fourth finger.

(4) The *anterior brachio-radial septum* (_Septum brachiale anticum radiale_), (Fig. 170 _s_‴) passes from the outer angle of the wall of the pectoral lymph-sac, over the inner head of the _M. triceps_ and _M. flexor carpi radialis_ to the thumb.

*b.* The *lymph-sacs* are enclosed by these three septa; they are four in number:--

[Illustration: Fig. 172.

Transverse section through the trunk in the region of the iliac lymph-sac.

_c_ Urostyle. _c_′ Skin. _o_ Muscles of abdominal wall. _1_ Dorsal lymph-sac. _3_ Lateral lymph-sac. _15_ Iliac lymph-sac. ]

(1) The *brachio-ulnar lymph-sac* (_Saccus brachialis ulnaris_), (Fig. 170 6) is situated between the first and second septa along the extensor and ulnar surfaces.

(2) The *brachio-radial lymph-sac* (_Saccus brachialis radialis_), (Fig. 169 7) is placed along the extensor and radial surfaces.

(3) The *anterior brachial lymph-sac* (_Saccus brachialis anticus_), (Fig. 170 8) lies on the flexor surface between the second and third septa; it is a long cavity and interrupted by connective-tissue bands, in which the tendon of the _M. sterno-radialis_ and the nerve and vessels are situated.

(4) The *axillary lymph-sac* (_Saccus axillaris_) corresponds to the iliac lymph-sac; it is bounded by the divisions of the ventral septum.

In the hand no large lymph-space exists; the skin is attached by numerous bands to the underlying structures.

C. The Lymph-sacs of the Hinder Extremity.

*a.* The *septa*.

(1) The *superior femoral septum* (_Septum femorale superius_), (Figs. 169 and 175 _f_′) is attached above to the inguinal septum near the posterior lymph-heart; and is continued, from this point, over the _M. vastus externus_ and along the _M. triceps_ to the knee.

[Illustration: Fig. 173.

Dissection to show the iliac lymph-sac.

_g_ M. glutaeus. _i.c._ M. ilio-coccygeus. _m.c._ M. cutaneus iliacus. _o_ M. obliq. abdom. externus. _r_ M. rectus. _S_ Dorsal septum. _S_′ Iliac septum. _S_‴ Portion of dorsal septum, which forms the roof of the iliac lymph-sac. _v_ M. vastus externus. * Aperture, by which the iliac lymph-sac communicates with the abdominal cavity. ]

(2) The *inferior femoral septum* (_Septum femorale inferius_), (Figs. 170 and 175 _f_″) runs from the inguinal septum near the point of insertion of the _M. rectus abdominis_, along the _M. rectus internus minor_ to the knee.

(3) The *intermediate femoral septum* (_Septum femorale intermedium_), (Figs. 169 and 175 _f_‴) passes from near the posterior lymph-heart over the _M. semimembranosus_ and the _M. rectus internus minor_ to join the inferior femoral septum.

[Illustration: Fig. 174.

Plan of attachments of the inferior femoral, inguinal, and perineal septa. ]

(4) The *tibio-femoral septum* (_Septum femoro-crurale_) is a circular band, separating the lymph-sacs of the thigh from the leg sac.

(5) The *septa* of the foot. At the ankle joint the skin is closely attached all round to the underlying parts. Along the outer border of the foot a septum is attached to the skin externally, and to the underlying parts, especially the _M. abductor longus digiti primi_, internally. A similar but weaker band is attached along the outer border of the foot, especially to the _M. adductor digiti quinti_.

*b.* The *lymph-sacs*.

(1) The *femoral lymph-sac* (_Saccus femoralis_), (Figs. 169, 170, 171, 175 9) covers the lower and outer surfaces of the thigh; it is bounded by the superior femoral and inferior femoral septa, and in front by the inguinal septum.

[Illustration: Fig. 175.

Transverse section of the thigh.

_b_ M. biceps. _f_′ Superior femoral septum. _f_″ Inferior femoral septum. _f_‴ Intermediate femoral septum. _H_ Skin. _ri_′ M. rectus internus major. _ri_‴ M. rectus internus minor. _s_ M. Sartorius. _sm_ M. semimembranosus. _ve_ M. vastus externus. _9_ Femoral lymph-sac. _10_ Suprafemoral lymph-sac. _11_ Interfemoral lymph-sac. ]

(2) The *suprafemoral lymph-sac* (_Saccus suprafemoralis_), (Figs. 169, 171, 175 _10_) lies on the upper surface of the thigh, between the superior and intermediate femoral septa; above it is bounded by the inguinal septum.

(3) The *interfemoral lymph-sac* (_Saccus interfemoralis_), (Figs. 169, 170, 175 _11_) is a narrow sac on the inner surface of the thigh, between the inferior femoral septum and the intermediate femoral septum. It covers the _M. rectus internus minor_, and is interrupted by numerous bands of tissue which pass from the surface of the muscle to the skin. It is, therefore, not a simple sac, but a very wide-meshed trabecular structure of connective-tissue. The sac is triangular in shape, with the base directed forwards at the inguinal septum.

(4) The *lymph-sac* of the *leg* is a simple sac enclosing the whole leg, bounded above by the tibio-femoral septum, and below by the attachment of the skin to the ankle.

(5) The *lymph-sacs* of the *foot*. On the dorsum of the foot the skin is free, and there is consequently a lymph-sac. On the plantar surface the skin is attached by numerous connective-tissue bands and thread-like tendons, particularly to the flexor tendons. The skin of the dorsal and plantar surfaces meet on the web and enclose a very rich anastomosis of lymph-capillaries.

*2.* The Lymph-Hearts.

The frog has two pairs of lymph-hearts, one pair anterior, the other posterior.

[Illustration: Fig. 176.

The anterior lymph-hearts.

_L_ The left anterior lymph-heart. _l.s._ M. levator scapulae. _N_ Brachial nerve. _t.s._ M. transverso-scapularis maior. _1–4_ Vertebrae numbered from before backwards. ]

A. The *anterior lymph-hearts* (Fig. 176). These organs lie, one on each side, behind the broad transverse processes of the third vertebra (Müller, Panizza, Priestley), in a deep triangular space formed by the separation of the fibres of the _M. intertransversarius_, between the transverse processes of the third and fourth vertebrae. Each heart is a rounded sac, slightly elongated anteriorly where it is connected with the subscapular vein. [The hearts receive lymph from the anterior part of the body and the surrounding parts, and empty their contents into the vertebral vein. Each of these hearts is supplied by a branch from the second spinal nerve (Volkmann, Eckhard, Schiff, Priestley).]

[Illustration: Fig. 177.

The posterior lymph-hearts.

_gl_ M. glutaeus. _ic_ M. ilio-coccygeus. _L_ Posterior lymph-hearts. _p_ M. pyriformis. _r_ M. rectus. _ve_ M. vastus externus. ]

B. The *posterior lymph-hearts* (Fig. 177) are situated on either side of the urostyle in the triangular spaces (Müller, Panizza, Priestley), bounded externally and above by the _M. glutaeus_, internally and above by the _M. coccygeo-iliacus_, below and externally by the origin of the _M. vastus externus_, and below by the _M. pyramidalis_. Each posterior heart is about two lines long and one broad, with its long axis placed antero-posteriorly; the outer surface is uneven and appears to be unequally dilated. The lymph-heart is closely attached to the surrounding parts, especially to the fascia covering the _M. ilii-coccygea_, and posteriorly to the _M. levator ani_ and the _M. pyramidalis_. [The posterior lymph-hearts receive lymph from the parts surrounding them, and from the hinder extremities, and forward it into the _V. iliaca communicans_.

The posterior lymph-hearts are each supplied by a branch from the corresponding coccygeal nerve (Waldeyer) by its dorsal branch. The lymph-hearts are also in close connection with the sympathetic system (Waldeyer).]