294 



THE ORGANS 



delinite manner relatively to the blood-vessels. The blood-vessels 

 of the liver must therefore be first considered. 



The BLOOD SUPPLY of the liver is peculiar in that in addition to the 

 ordinary arterial supply and venous return, which all organs possess, 

 the liver receives venous blood in large quantities through the portal 

 vein. There are thus two afferent^vessels, the hepatic artery and the 

 portal vein, the former^~carrying arterial bloody the latter venous 

 blood from the intestine. Both vessels enter the liver at the hilum 

 and divide into large interlobar branches, which follow the connective- 

 tissue septa between the lobes. From these are given off interlobular 

 branches, which run in the smaller connective-tissue septa between 



the lobules. From the interlobular 

 branches of the portal vein arise veins 

 which are still interlobular and encircle 

 the lobules. These send off short 

 branches which pass to the surface of 

 the lobule, where they break up into 

 a rich intralobular capillary network. 

 These intralobular capillaries all con- 

 verge toward the center of the lobule, 

 where they empty into the central vein 

 (Fig. 194). The central veins are the 

 smallest radicles of the hepatic veins, 

 which are the efferent vessels of the 

 liver. Each central vein begins at the 

 apex of the lobule as a small vessel little 

 larger than a capillary. As it passes 

 through the centre of the long axis of 

 the lobule the central vein constantly 

 receives capillaries from all sides, and, 

 increasing in size, leaves the lobule at 

 its base. Here it unites with the central veins of other lobules to 

 form the sublobular vein which is a bfarseli of the hepatic (Fig. 205). 

 The hepatic artery accompanies the portal vein, following the 

 branchings of the latter through the interlobar and interlobular con- 

 nective tissue, where its fmer twigs break up into capillary networks. 

 Some of these capillaries empty into the smaller branches of the portal 

 vein; others enter the lobules and anastomose with the intralobular 

 portal capillaries. 



The MAIN EXCRETORY DUCT- — hepatic duct — leaves the liver at the 



Fig. 196. — Portal Canal. X315 

 (Klein and Smith.) a, Hepatic 

 artery; F, portal vein; i, bile duct. 



