596 THE VEINS 



and left common iliac veins at the fifth luml)ar vertebra, above the terminal part 

 of the aorta antl chiefly to the right of the metlian plane. 



The mode of origin is variable. In some cases there is a common trunk formed by the 

 union of the two internal iliac veins so that the arrangement resembles the termination of the 

 aorta. In other cases the internal iliac ^•ein does not exist. 



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 downward along the inner border of the right 

 lobe and the parietal surface of the liver, largely embedded in the gland substance, 

 and passes through the foramen vense cava of the diaiihragm. It then runs for- 

 ward and somewhat downward between the mediastinal 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. It receives the following tributaries: 



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

 usually empty into the vena cava. Sometimes the corresponding veins of opposite 

 sides unite to form a common trunk. The first communicate with the vena azj'gos. 



2. The spermatic veins (Vv. spermaticse internae) (Fig. 450) accompany the 

 arteries of like name. In the spermatic cord they form the pampiniform plexus 

 about the artery and nerves. Their termination is variable. The right one com- 

 monly 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. 



2a. 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. 



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

 and thin-walled. Tlie right vein passes inward 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 inward 

 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 open 

 directly into the vena cava. 



4. 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 vessels 

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

 discharge into its embedded i)art. 



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

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

 join the vena cava as it lies in the caval opening. 



In some cases there is a small middle sacral vein (V. sacralis media), a satellite of the artery. 

 It opens into the angle of junction of the common iliac veins or into one of the latter. 



THE PORTAL VEIN 



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

 the viscera by the gastric, si)lenic, and mesenteric arteries. Its peripheral tribu- 

 taries correspond closely with the branches of the arteries, but the terminal trunks 

 do not. The vein is formed behind the pancreas and below the jjosterior vena cava 

 by the confluence of the anterior and posterior mesenteric and splenic veins. It 

 passes forward, traverses the ix)sterior i)art of the pancreas very obliquely, inclines 



