THE PORTAL VEIN 693 



• "^"J^^"?*^ °- °"^'", '•?■ '^'^"able. In some cases there is a common trmik formed bv the 

 umon of the two mternal ihac veins so that the arrangement resembles the termination of the 

 aorta In other cases the mternal ihao vem does not exist. Exceptionally there is a small middle 

 sacral vem on the middle of the pelvic surface of the sacrum. It opens at the angle of divergence 

 01 the common iliac vems. &^ ^^ 



It passes forward on the ventral face of the psoas minor to the right of the 

 abdominal aorta. At the last thoracic vertebra it separates from the aorta and 

 runs forward between the right crus of the diaphragm and the pancreas till it 

 reaches the liver. Here it inclines ventrally along the medial border of the right 

 lobe and on the parietal surface of the liver, largely embedded in the gland sub- 

 stance, and passes through the foramen vena cava of the diaphragm. It then runs 

 forward and somewhat ventrally between the intermediate lobe and the main mass 

 of the right lung at the upper margin of a special fold of the right pleura, accom- 

 panied by the right phrenic nerve, and opens into the posterior part of the right 

 atrium opposite the fifth intercostal space. It receives the following tributaries: 



1. The phrenic veins (Vv. phrenicse), two or three in number, return the blood 

 from the diaphragm. They are very large in comparison with the arteries, and 

 join the vena cava at the foramen venae cavse. 



2. The lumbar veins (Vv. lumbales) correspond to the arteries. Five pairs 

 usually empty into the posterior vena cava. Sometimes the corresponding veins 

 of opposite sides unite to form a common trunk. The first communicate with the 

 vena azygos or hemiazygos, and the last usually enters the common iliac vein. 



3. The internal spermatic veins (Vv. spermaticae internse) (Fig. 575) accompany 

 the arteries of like name. In the spermatic cord they form a very rich network, the 

 pampiniform plexus (Plexus pampiniformis) about the artery and nerves. Their 

 termination is variable. The right one commonly joins the vena cava near the 

 renal vein, often by a common trunk with the left one. Frequently the left vein 

 joins the left renal, and sometimes the right one ends similarly. 



3 a. The utero-ovarian veins are much larger than the preceding and are 

 satellites of the arteries in the broad ligaments. The ovarian branch is plexiform 

 near the ovary. The uterine branches form a rich plexus in the wall of the uterus. 

 The trunk is very short and terminates like the corresponding vein of the male. 



4. The renal veins (Vv. renales), satellites of the arteries, are of large caliber 

 and thin walled. The right vein passes medially and backward on the ventral face 

 of the kidney, between the artery in front and the ureter behind. It joins the vena 

 cava above the right adrenal. The left vein is somewhat longer. It passes medially 

 at first like the right one, then bends around the posterior end of the adrenal, crosses 

 the origin of the renal artery, and opens into the vena cava a little further back than 

 the right one. They receive veins from the adrenals, but some adrenal veins (Vv. 

 adrenales) open directly into the vena cava. 



5. The hepatic veins (Vv. hepaticae) return the blood from the liver, and open 

 into the vena cava as it lies in the groove in the liver. Three or four large veins 

 open into the vena cava just before it leaves the liver, and numerous small ones 

 discharge into its embedded part. 



Of the foregoing, the phrenic and lumbar veins are termed parietal radicles 

 (Radices parietales), and the remainder are visceral radicles (Radices viscerales). 



THE PORTAL VEIN 



The portal vein (V. ports) is a large trunk which returns the blood carried to 

 the viscera by the gastric, splenic, and mesenteric arteries; its average diameter is 

 a little more than an inch (ca. 3 cm.). Its peripheral tributaries correspond closely 

 with the branches of the arteries, but the trunks do so in part only. The vein is 

 formed behind the pancreas and below the posterior vena cava by the confluence 

 of the anterior and posterior mesenteric and splenic veins. It passes forward, 



