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right inferior phrenic vein, the right suprarenal vein, the right and left renal veins, the right internal spermatic vein, and the right and left lumbar veins.

Venæ Hepaticæ (Fig. 792).—The hepatic veins convey blood which has passed through the liver from the portal veins and from the hepatic artery, and they open into that portion of the inferior vena cava which lies immediately below the diaphragm, and behind the right lobe of the liver. They form two groups, an upper group of two or three large trunks, and a lower group of smaller veins.

The upper group occasionally consists of only two veins, a right and a left; more frequently there are three vessels, a right, a left, and a middle vein, and in the latter case the middle vein issues from the caudate lobe (Spigelian).

The veins of the lower group vary in number from six to twenty ; they return blood from the right and caudate lobes.

The hepatic veins commence in the interiors of the lobules of the liver as central veins; the central veins issue from the upper and posterior aspects of the lobules, and unite together to form interlobular veins; and the interlobular veins unite with one another, as they converge towards the posterior surface of the liver, to form the larger hepatic veins.

Venæ Phrenicæ Inferiores.—The inferior phrenic veins are formed by tributaries which issue from the substance of the diaphragm. The right inferior phrenic vein terminates in the upper part of the inferior vena cava. The left vein passes posterior to the wesophagus, and usually terminates in the left suprarenal vein.

Venæ Suprarenales.—A single suprarenal vein issues from the hilum on the anterior surface of each suprarenal gland; the right vein terminates in the inferior vena cava; the left usually ends in the left renal vein, but sometimes it opens directly into the inferior vena cava.

Venæ Ronales.—Each renal vein is formed by the union of five or six tributaries which issue from the hilum of the kidney, where they lie anterior to or are intermingled with the corresponding arteries.

The right renal vein is about 25 mm. (one inch long); it passes posterior to the descending part of the duodenum, and terminates in the right side of the inferior vena cava.

The left renal vein is about 75 mm. long. It crosses anterior to the left psoas major, the left crus of the diaphragm, and the aorta immediately below the superior mesenteric artery. It lies behind the pancreas and the ascending part of the duodenum, and, running above the transverse part of the duodenum, terminates in the left side of the inferior vena cava. The left testicular or ovarian vein, according to the sex, and almost invariably the left suprarenal vein, open into it.

Vonæ Lumbales.—There are usually four lumbar veins on each side, one with each lumbar artery; the vein with the subcostal artery is not included in this number. By their anterior and posterior branches the lumbar veins drain the lateral and posterior walls of the abdomen. The anterior branches commence in the lateral walls of the abdomen, where they communicate with the superior and inferior epigastric veins. The posterior divisions issue from the muscles of the back, in the lumbar region, and receive tributaries from the spinal plexuses. The main stems pass forwards on the bodies of the vertebræ; on each side they run postero-medial to the psoas major muscle, whilst those of the left side also pass posterior to the aorta. They terminate in the posterior part of the inferior vena cava. Not uncommonly the corresponding veins of opposite sides unite together to form a single trunk which enters the back of the inferior vena cava. All the lumbar veins, of each side, are united together by a longitudinal anastomosing vessel, the ascending lumbar vein.

The Ascending Lumbar Vein.—Each ascending lumbar vein passes upwards, between the psoas major and the roots of the transverse processes of the lumbar vertebræ. It commences in the lateral sacral vein of the same side, anastomoses with the ilio-lumbar vein, connects the lumbar veins together, receives tributaries from the anterior external vertebral plexus and anastomoses with the inferior vena cava and the renal vein. The right ascending lumbar vein terminates in the azygos and the left in the hemiazygos vein.

Vonæ Testiculares.—The testicular veins, on each side, issue from the testis and epididymis and form a plexus, the pampiniform plexus. The plexus is one of the constituents of the spermatic cord, and consists of from eight to ten veins, most of which lie anterior to the ductus deferens; it passes upwards through the scrotum and inguinal canal, and, near the abdominal inguinal ring, terminates in two main trunks which ascend, with the corresponding testicular artery, for some distance, receiving tributaries from the ureter; ultimately the two veins unite together and a single terminal vein is formed. The terminal testicular vein on the right side opens into the inferior vena cava, that on the left side into the left renal vein. The left testicular vein is longer than the right, the left testis being lower than the right, and the termination in the left renal vein being at a higher level than the termination of the right vein in the inferior vena cava. The testicular veins, on each side, lie anterior to the psoas major muscle and the ureter. They are covered by peritoneum, and they are crossed on the right side by the termination of the ileum and the third part of the duodenum, and on the left side by the iliac colon and the lower part of the pancreas. They are provided with valves, one of which usually lies at the terminations of each vein, but, occasionally, the valve at the orifice of the left testicular vein is absent.

Vena Ovaricæ.—The ovarian veins, on each side, issue from the hilum in the anterior border of the ovary. They pass between the layers of the broad ligament, where they anastomose freely and form the pampiniform plexus, which extends, laterally, towards the upper margin of the pelvis minor. From the plexus two veins issue which accompany the corresponding ovarian artery; they pass anterior to the external iliac artery, and then upwards, behind the peritoneum and anterior to the psoas major muscle and ureter. The veins of the right side, like the corresponding testicular veins, also pass behind the termination of the ileum and the third part of the duodenum; whilst the left veins, near the margin of the pelvis minor, pass behind the commencement of the pelvic colon.

The two veins on each side ultimately fuse together to form a single terminal vein which ends, on the right side in the inferior vena cava, aud on the left side in the left renal vein.

VENÆ ILIACÆ COMMUNES.

The common iliac veins (Figs. 777 and 792), right and left, are formed by the union of the corresponding external iliac and hypogastric veins. Each commences at the superior aperture of the pelvis minor, immediately posterior to the upper part of the hypogastric artery of its own side, and both vessels pass upwards to the right side of the body of the fifth lumbar vertebra, at the upper part of which, posterior and lateral to the right common iliac artery, they unite together to form the inferior vena cava.

The right common iliac vein is much shorter than the left; it passes anterior to the obturator nerve and the ilio-lumbar artery, and at first posterior and then somewhat to the lateral side of the corresponding common iliac artery.

The left common iliac vein is much longer than the right, and is also placed more obliquely. It passes upwards and to the right, anterior to the body of the fifth lumbar vertebra, and the middle sacral artery. For some distance it runs along the medial side of the left common iliac artery, and then passes posterior to the right common iliac artery. It also passes posterior to the mesentery of the pelvic colon and the superior hæmorrhoidal vessels.

Tributaries.- Each common iliac vein receives the corresponding external iliac, hypogastric and ilio-lumbar veins. The left common iliac vein receives, in addition, the middle sacral vein.

The ilio-lumbar veins receive tributaries from the iliac fossa, from the lower parts of the vertebral muscles, and from the vertebral canal. There is a single vein on each side which accompanies the corresponding artery. It passes posterior to the psoas major muscle and terminates in the corresponding common iliac vein.

Vena sacralis Media.—The venæ comites of the middle sacral artery commence by the union of tributaries which issue from the venous plexus in front of the sacrum,

through which they communicate with the lateral sacral veins and receive blood from the interior of the sacral canal. They unite, above, into a single middle sacral vein, which terminates in the left common iliac vein.

Vena Hypogastrica.—The hypogastric vein (Fig. 777) is a short trunk formed by the union of tributaries which correspond to all the branches of the hypogastric artery, with the exception of the umbilical and the ilio-lumbar branches.

It commences at the upper border of the greater sciatic notch, and ascends the aperture of the pelvis minor; there it unites with the external iliac vein to form the common iliac vein. It lies immediately postero-medial to the hypogastric artery, is crossed laterally by the obturator nerve, and is in relation medially, on the lett side with the pelvic colon, and on the right side with the lower part of the ileum.

Tributaries.—The tributaries, which are numerous, are conveniently divisible into extra-pelvic and intra-pelvic groups.

The extra-pelvic tributaries are all parietal, and include the obturator, internal pudendal, inferior, and superior glutæal veins.

Obturator Vein.—This vein is formed by the union of tributaries which issue from the hip-joint and from the muscles of the proximal and medial part of the thigh. It enters the pelvis minor through the obturator canal, runs backwards, along the latera. wall of the pelvis minor, lying medial to the pelvic fascia, immediately below the corresponding artery, and, passing between the hypogastric artery on the lateral side and the ureter on the medial side, it terminates in the hypogastric vein.

Inferior Gluteal Veins (0.T. Sciatic).—The venæ comites of the inferior gluteal artery commence in the subcutaneous tissues on the back of the thigh; they ascend with the artery, and pass into the buttock on the deep aspect of the glutæus maximus, where they receive numerous tributaries from the surrounding muscles. Entering the pelvis, through the greater sciatic foramen, they unite into a single vessel, which terminates in the lower and anterior part of the hypogastric vein below the termination of the obturator vein.

Superior Gluteal Veins (0.T. Glutæal).-The venæ comites of the superior gluteal artery are formed by tributaries which issue from the muscles of the buttock. They accompany the artery through the greater sciatic foramen, and terminate in the hypogastri vein; they frequently unite together before reaching their termination.

Internal Pudendal Veins. — The venæ comites of the internal pudendal artery commence by tributaries which emerge from the pudendal plexus, which lies below and posterior to the arcuate ligament of the pubis and constitutes the anterior part of the prostatic plexus They receive blood from the corpus cavernosum penis, or the corpus cavernosum clitoridis. by the deep vein of the penis or clitoris. They follow the course of the internal pudendal artery, and usually join together into a single vessel (the internal pudendal vein) which terminates in the hypogastric vein. They receive as tributaries the veins from the bulb, the perineal and inferior hæmorrhoidal veins, and veins from the muscles of the buttock.

The inferior hæmorrhoidal veins, which commence in the substance of the external sphincter of the anus and in the walls of the anal canal, anastomose with the middle and superior. hæmorrhoidal veins, and consequently connect the lowest parts of the portal and vena caval systems together.

The intra-pelvic tributaries of the internal iliac vein are either (a) parietal or (6) visceral; the former comprises the lateral sacral veins, the latter includes the efferent vessels from the plexuses around the several pelvic viscera.

(a) Parietal: Lateral sacral veins accompany the lateral sacral arteries, and terminate on each side in the postero-medial wall of the corresponding hypogastric vein.

(6) Visceral tributaries are derived from the rectum and from the plexuses associated with the uterus, vagina, bladder, and prostate. They include the middle hæmorrhoidal, the uterine, the vaginal, and the vesical veins.

The middle hæmorrhoidal veins are very irregular; sometimes they cannot be distinguished. When present they are formed by tributaries which commence in the submucous tissue of the rectum, where they communicate with the'superior and inferior hæmorrhoidal veins in the hæmorrhoidal plexus ; they pass through the muscular coat, and fuse together to form two middle hæmorrhoidal veins, right and left, each of which runs laterally, beneath the peritoneum, on the upper surface of the levator ani, to terminate in the corresponding hypogastric vein. In the male each middle hæmorrhoidal vein receives tributaries from the seminal vesicle and ductus deferens of its own side.

Uterine Plexuses and Veins.—The uterine plexuses lie along the borders of the E uterus; they receive tributaries, which are entirely devoid of valves, from the uterus; and they communicate above with the ovarian, and below with the vaginal plexuses.

The uterine veins, usually two on each side, issue from the lower parts of the uterine plexuses, above their communications with the vaginal plexuses. At first the uterine veins, on each side, lies in the medial part of the base of the broad ligament, above the lateral fornix of the vagina and the ureter; then they pass backwards, accompanying the corresponding artery, in a fold of peritoneum which lies between the back of the broad ligament and the recto-uterine fold; finally they ascend in the floor of the ovarian fossa, and terminate in the corresponding hypogastric vein.

Vaginal Plexuses and Vaginal Veins.— The vaginal plexuses lie at the sides of the vagina. They receive tributaries from the walls of the vagina, and communicate with the uterine plexuses above, and with the veins of the bulb below; anteriorly, with the vesical plexus; and posteriorly with the veins which issue from the middle and lower parts of the hæmorrhoidal plexus. A single vaginal vein issues from the upper part of the vaginal plexus on each side; it accompanies the corresponding artery, and terminates in the hypogastric vein.

Superior Vesical Plexus.—The superior vesical plexus of veins lies on the outer surface of the muscular coat of the bladder, at the fundus and the sides. It receives tributaries from the mucous and muscular walls, and its efferent vessels terminate in the prostatico-vesical plexus in the male, and in the inferior vesical plexus in the female.

Prostatico-vesical Plexus.-- This plexus is distributed around the prostate and the neck of the bladder, and is enclosed between the proper fibrous capsule of the prostate and its sheath of recto-vesical fascia. Anteriorly it is continuous with the pudendal plexus which receives the dorsal vein of the penis ; postero-superiorly it communicates with the superior vesical plexus, and receives tributaries from the seminal vesicles and deferent ducts. One or more efferent vessels pass from it on each side and open into the corresponding hypogastric vein.

The inferior vesical plexus of the female, which represents the prostatico-vesical plexus of the male, surrounds the upper part of the urethra and the neck of the bladder. It is continuous with the pudendal plexus which receives the dorsal vein of the clitoris, and its efferent vessels terminate in the hypogastric vein.

Dorsal Veins of the Penis.—There are two dorsal veins of the penis — the superficial and the deep.

The superficial dorsal vein receives tributaries from the prepuce, and runs backwards, immediately beneath the skin, to the symphysis, where it divides into two branches which terminate in the superficial external pudendal veins.

The deep dorsal vein lies on the dorsum of the penis, deep to the deep fascia. It commences in the sulcus behind the glans, by the union of numerous tributaries from the glans and the anterior parts of the corpora cavernosa penis; and it runs backwards in the mid-dorsal line, in the sulcus between the corpora cavernosa penis from which it receives many additional tributaries. At the root of the penis the vein passes between the two layers of the suspensory ligament, and then between the arcuate ligament and the deep transverse ligament of the perineum, where it lies above the membranous part of the urethra. It terminates by dividing into two branches which join the pudendal plexus.

The dorsal vein of the clitoris in the female has a similar course to that of the deep dorsal vein of the penis in the male. It terminates in the pudendal plexus.

THE VEINS OF THE INFERIOR EXTREMITY. The veins of the inferior extremity, like those of the superior extremity, are arranged in two groups, the superficial and the deep; and in the lower as in the upper limb the deep veins are associated with the arteries as venæ comites, whilst the trunks of the superficial veins, which lie, at first, in the subcutaneous tissues ultimately terminate in the deep veins. There is, therefore, a general similarity in the arrangement of the veins of the upper and the lower limbs, but there are differences in the details of the arrangement which are of some importance. Thus, in the superior extremity, there are two deep veins with each artery from the fingers to the root of the limb, where a single trunk, the axillary vein, is formed ; but in the inferior extremity each main artery has two venæ comites only as far as the middle of the limb, where a single trunk is frequently formed. That vessel, the popliteal vein, is the commencement of the main venous stem of the lower extremity; it is continued proximally, through the thigh, as the femoral vein, and along the upper margin of the pelvis ininor as the external iliac vein, which terminates by uniting with the hypogastric vein to form the common iliac vein.

Further, the superficial veins of the upper limb are more numerous than those of the lower limb, for in the arm there are two main superficial veins, and in the thigh only one.

In the upper limb the blood which passes through the superficial veins is poured into the efferent trunk vein at the root of the limb—that is, into the axillary vein ; but in the lower limb the blood from the superficies of the lateral parts of the leg and foot passes into the commencement of the main efferent vein, the popliteal vein, at the middle of the limb—that is, in the region of the knee, whilst the blood from the superficial parts of the medial aspect of the lower limb is poured into the femoral vein near the root of the limb in the upper part of the femoral trigone.

In addition to the above-mentioned differences in the general arrangement of the veins of the superior and the inferior extremities, it must be noted also that in the superior extremity all the blood of the limb, both that from the shoulder-girdle region as well as that from the free portion of the limb, is returned to the main efferent venous trunk; but in the inferior extremity the greater part of the blood from the region of the pelvic girdle, and a considerable portion from that of the thigh, is returned by the glutæal, obturator, and pudendal veins to the hypogastric vein, which is not the main efferent vein of the inferior extremity.

THE DEEP VEINS OF THE INFERIOR EXTREMITY. All the arteries of the lower limb, except the popliteal and femoral trunks, are accompanied by two venæ comites. They usually lie one on each side of the artery; they are connected with one another by transverse channels which pass across the line of the artery, and they are provided with numerous valves.

Vena Poplitea.—The popliteal vein (Figs. 776, 780, 781) is formed, at the distal border of the popliteus muscle, by the union of the venæ comites of the anterior and posterior tibial arteries. At its commencement it lies to the medial side of and somewhat superficial to the popliteal artery, and to the lateral side of the tibial (O.T. internal popliteal) nerve. As it runs through the popliteal fossa it inclines towards the lateral side of the artery, and in the middle of the space it is directly posterior to the artery, separating the artery from the tibial nerve, which is still more posterior, whilst at the proximal end of the space it is to the lateral side of the artery, and still between it and the tibial nerve. It then passes through the adductor magnus muscle and becomes the femoral vein.

The popliteal vein, which is provided with two or three bicuspid valves, is closely bound to the artery by a dense fascial sheath. Not uncommonly there are one or more additional satellite veins which anastomose with the popliteal vein, and in those cases the artery is more or less completely surrounded by venous trunks.

Tributaries. In addition to the venæ comites of the anterior and posterior tibial arteries, it receives tributaries which correspond with the branches of the popliteal artery, and it also receives one of the superficial veins of the leg, viz., the small saphenous vein.

Vena Femoralis.—The femoral vein is the direct continuation of the popliteal vein. It commences at the junction of the middle and distal thirds of the thigh, at the opening in the adductor magnus muscle. It then ascends, through adductor canal (Hunter's), and through the femoral trigone, and terminates, a little to the medial side of the middle of the inguinal ligament (Poupart's), by becoming the external iliac vein.

In the adductor canal it lies at first postero-lateral to the femoral artery, and anterior to the adductors magnus and longus which separate it from the profunda vessels. In the distal part of femoral trigone it is postero-medial to the artery, and immediately anterior to the profunda vein which separates it from the profunda artery, but in the proximal part of the femoral trigone it is directly on the medial side of the femoral artery. About 37 mm. (one and a half inches) below

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