THE ABDOMEN AND ITS CONTENTS 107 



B. POSTCAVA 



(Vena cava inferior, Figs. 27, 29) 



The postcava arises principally by the confluence of the 

 internal- and external iliacs, renal, and hepatic veins. 

 Its principal branches are essentially as in the abdominal aorta ; 

 however, the hepatic veins are vastly larger than the hepatic 

 artery, and there are no systemic venous branches to correspond 

 to the celiac (42) and superior mesenteric (47) arteries. The 

 blood carried to the portal organs by the branches of these 

 two arteries (42, 47) is collected by the hepatic portal system 

 and by this vein conveyed to the liver. 



C. HEPATIC PORTAL SYSTEM 



The hepatic portal vein (portal vein; Figs. 30, 31) and its 

 tributaries and hepatic branches (Fig. 31) comprise the hepatic 

 portal system. This venous system drains the portal organs 

 (the small intestine, large intestine, stomach, spleen, and 

 pancreas) and is the only instance in the rabbit, or man, in 

 which a vein arises by capillaries and ends in capillaries. This 

 arrangement makes it possible for the portal vein to convey the 

 digested food materials, except fats (which are conveyed by 

 the lymphatic system directly to the precaval system, in all 

 mammals) to the liver. After a sojourn in the liver, most of 

 the carbohydrates and proteins undergo a chemical change. 

 The liver receives the major portion of its blood from the 

 hepatic portal vein and the remainder from the hepatic artery 

 (45). The student should be certain to get the hepatic portal 

 system well in mind, for its physiological aspects are exceedingly 

 important. 



Method: Further study of the hepatic portal vein should be 

 delayed until the stomach has been studied, p. 112. It is 

 usually possible to inject a considerable part of the hepatic 

 portal vein, especially that in the mesentery of the small 

 intestine, in a preserved rabbit with the starch mixture men- 



