Part 181

These (V. iliacæ communes) are two very large but short trunks which result from the union of the internal and external iliac veins of each side at the sacro-iliac articulation. The left one is the longer and crosses obliquely over the terminal part of the aorta. The chief tributaries of each are as follows:

1. The last =lumbar vein=.

2. The =circumflex iliac veins= (Vv. circumflexæ ilium profundæ) are the two satellites of each corresponding artery, on either side of which they are placed. They may open directly into the posterior vena cava or into the external iliac vein.

3. The =ilio-lumbar vein= (V. iliolumbalis) may open into the common iliac, the external iliac, or the internal iliac vein.

THE INTERNAL ILIAC VEINS

The =internal iliac= or =hypogastric veins= (Vv. hypogastricæ), right and left, are usually formed by the confluence of lateral sacral, gluteal, and internal pudic veins. The obturator vein may open into them also. They are short trunks and are smaller than the external iliac veins. The tributaries correspond in general to the branches of the three arteries of like names. The internal pudic veins receive affluents from the venous plexuses of the prepuce and penis in the male; of the mammary gland, vulva, vagina, and vestibular bulb in the female.

THE VEINS OF THE PELVIC LIMB

The =external iliac vein= (V. iliaca externa) (Figs. 450, 451) lies behind the corresponding artery at the brim of the pelvis. It is the upward continuation of the femoral vein, and unites at the sacro-iliac joint with the internal iliac to form the common iliac vein. Its tributaries are as follows:

1. The =obturator vein= (V. obturatoria) is a satellite of the artery and usually opens into the external iliac at the insertion of the psoas minor. Its radicles anastomose with those of the internal and external pudic veins (Figs. 451, 455).

2. The =iliaco-femoral= or =external circumflex veins= (Vv. circumflexæ femoris laterales) are the two satellites of the homonymous artery. They open a little higher than the obturator.

The =femoral vein= (Figs. 450, 451) lies behind the artery in the upper part of the thigh, external to it lower down. Its chief tributaries are:

1. A very large but short trunk formed by the union of the deep femoral and the external pudic vein. The =deep femoral vein= (V. profunda femoris) corresponds otherwise to the artery. The =external pudic vein= (V. pudenda externa) arises chiefly from a rich plexus of large veins situated above and along the sides of the penis and prepuce in the male, the mammary glands in the female. It passes through a foramen in the anterior part of the tendon of origin of the gracilis and runs outward in the subpubic groove behind the pectineus to unite with the deep femoral vein. The right and left veins are connected by a large transverse anastomosis and each has a large connection with the obturator vein. Each receives the =posterior abdominal vein= (V. epigastrica caudalis) which accompanies the artery of like name. The =subcutaneous abdominal vein= (V. abdominalis subcutanea) arises in the skin and panniculus of the ventral abdominal wall, anastomoses with the internal and external thoracic and deep abdominal veins, and joins the external pudic or posterior abdominal vein.

A small vein accompanies the external pudic artery in the inguinal canal.

2. The =anterior femoral vein= (V. femoris cranialis) accompanies the artery.

3. The =saphenous vein= (V. saphena) (Figs. 451, 458, 460) arises at the inner side of the flexion surface of the tarsus as the upward continuation of the internal metatarsal vein. Its course is distinctly visible. It ascends on the subcutaneous surface of the tibia and the popliteus muscle, inclosed between layers of the deep fascia, inclines a little backward to the proximal part of the leg, then deviates slightly forward, runs upward on the gracilis, passes between that muscle and the sartorius, and joins the femoral or the external pudic vein. On the upper part of the capsule of the hock joint it forms an arch with the anterior tibial vein. The vein has numerous valves. The satellite artery is relatively small and lies in front of the vein as far as the junction with the recurrent tibial vein, which it accompanies on the leg. It receives the =recurrent tibial vein= (V. recurrens tibialis) at the proximal fourth of the leg. This vessel arises at the inner surface of the tarsus and forms an arch with the posterior tibial vein at the level of the tuber calcis. It ascends in the furrow in front of the gastrocnemius tendon, inclines forward at the proximal third of the leg, and joins the saphenous vein at an acute angle. It has numerous valves. A smaller vein from the anterior face of the metatarsus joins the saphenous at the hock.

4. =Muscular branches= which correspond to the arteries.

5. The =posterior femoral= or =femoro-popliteal= vein (V. femoris caudalis) is a satellite of the artery. It receives the =recurrent tarsal= or =external saphenous vein= (V. tarsea recurrens), which arises at the outer side of the hock, ascends on the deep fascia of the external surface of the leg in front of the tendo Achillis, passes between the biceps femoris and semitendinosus, and joins the posterior femoral vein. It is connected with the recurrent tibial vein by a large anastomotic branch which crosses in front of the tuber calcis. Usually a branch from it ascends along the great sciatic nerve and anastomoses with the obturator vein.

The =popliteal vein= (V. poplitea) lies along the inner side of the artery (Fig. 459). It is formed by the confluence of anterior and posterior tibial veins.

Two =anterior tibial veins= (Vv. tibiales anteriores) usually accompany the artery of like name; the outer vein is much the larger. In other cases there is a single large vein in the proximal part of the leg, two lower down. They arise from a number of anastomosing radicles on the front of the capsule of the hock joint, chiefly as the continuation of the perforating tarsal vein. The origin of the chief vein is connected with the saphenous by a large anastomotic branch.

The =posterior tibial vein= (V. tibialis posterior) is commonly double (Fig. 458). It arises at the level of the tuber calcis, where it has a communication with the recurrent tibial vein. It is a satellite of the artery.

The =internal= or =great metatarsal vein= (V. metatarsea dorsalis medialis) (Figs. 458, 460) arises from the venous arch above the sesamoids at the fetlock, but is practically the upward continuation of the internal digital vein. It ascends along the inner border of the deep flexor tendon, then in the groove on the inner aspect of the proximal part of the large metatarsal bone to the capsule of the hock joint, and is continued by the saphenous vein.

The =external metatarsal vein= (V. metatarsea plantaris lateralis) arises from the venous arch above the fetlock, but appears to be the upward continuation of the external digital vein. It ascends along the outer border of the deep flexor tendon in front of the plantar nerve, and is connected with the deep metatarsal vein at the proximal part of the metatarsus by a transverse branch. It then passes upward along the deep flexor tendon in relation to the plantar nerves and the inner tarsal artery and is continued by the recurrent tibial vein.

The =deep metatarsal vein= (V. metatarsea plantaris medialis) arises from the plantar venous arch, passes forward between the branches of the suspensory ligament, and ascends on the posterior face of the large metatarsal bone. At the proximal end of the metatarsus it is connected with the external metatarsal vein by a transverse branch. It then passes (as the perforating tarsal vein) through the vascular canal of the tarsus and forms the chief radicle of the anterior tibial vein.

The =plantar venous arch= (Arcus venosus plantaris) and the digital veins are arranged like those of the thoracic limb.

The Lymphatic System

The =lymphatic system= (Systema lymphaticum) is subsidiary to the venous part of the circulatory system, from which it arises in the embryo. It consists of the lymph vessels and glands.

The =lymph vessels= (Vasa lymphatica) contain a colorless fluid, the lymph, which contains numerous lymphocytes. They resemble the veins in structure but have thinner walls and are provided with more numerous valves. The vessels are sacculated opposite the segments of the valves and have a characteristic beaded appearance when distended. The collecting lymph vessels do not usually form rich plexuses, as veins often do, their branching is more limited and less tree-like than that of the blood-vessels, and their caliber therefore increases less from the periphery toward their termination. All of the lymph is ultimately carried into the venous system by two trunks, the =thoracic duct= and the =right lymphatic duct=. Almost all of the lymph passes through at least one group of lymph glands before entering the blood-vascular system.

The =lymph glands= or =nodes= (Lymphoglandulæ) are intercalated in the course of the lymph vessels. They vary widely in size, some being microscopic, others several inches in length. In form they may be globular, ovoid and flattened, elongated, or irregular. In certain situations they are aggregated into groups, and a knowledge of the position of these and the territory drained into them is important. It is convenient, when possible, to indicate their position with regard to arteries on the course of which they are placed. In color they are usually gray or yellowish-brown in the dead subject, pink or reddish-brown during life, but this varies according to their position and functional state. The bronchial glands are often blackened by infiltration with carbon. The mesenteric glands are creamy or white while the chyle is passing through, but pink at other times. Vessels which carry lymph to a gland are called =afferent=; the =efferent= vessels which convey it away are larger and fewer. Each gland has a depression, the =hilus=, at which the blood-vessels enter and the efferent lymph vessels emerge.