PORTAL VEIN. 263 



cava, the left into the left renal vein. The left spermatic 

 has comparatively few valves. The renal veins return 

 the blood from the kidneys ; the supra-renal from the 

 supra-renal capsules. 



The portal vein is formed by the superior and infe- 

 rior mesenteric, the gastric, and splenic. It drains the 

 intestinal tract, enters the liver, breaks up into a system 

 of capillaries, which become confluent, and finally ter- 

 minate in three hepatic, which empty into the ascending 

 vena cava. At the transverse fissure of the liver the 

 portal vein divides into a right and left branch, which give 

 off the vaginal branches ; these send off the interlobular; 

 and the branches of the interlobular are the lobular, which 

 are the smallest branches of the portal system. They 

 pass through the lobule, empty into the central or 

 intra-lobular vein, which empties into the sublobular; 

 these open into the small hepatic, which, by joining to- 

 gether, form the three or five hepatic veins that empty 

 into the ascending vena cava as it lies in the pos- 

 terior fissure of the liver. The innominate veins, two 

 in number, are formed by the union of the internal 

 jugular and the subclavian of each side. The right is 

 shorter than the left, and joins the left innominate 

 behind the costal cartilage of the first rib on the right 

 side, forming the descending vena cava. The innomi- 

 nate veins receive the internal mammary, inferior thy- 

 roid, and superior intercostal veins. 



The descending or superior vena cava, formed by the 

 union of the two innominates, is about three inches 

 long, and terminates in the superior posterior part of the 

 right auricle. The superior vena cava receives the vena 

 a/ygos major, which runs along the right side of the 

 bodies of the dorsal vertebrae and receives the vena 

 azygos minor and the intercostal veins. The veins of 



