THE Dir.F.STIVK S^-STEM 



29; 



hilum near the entrance of the portal vein and hepatic arter}-. Within 

 the liver the duct divides and subdivides, giving off interlobar^ and 

 these in turn interlobular branches. These ramify in the connective 

 tissue, where they always accompany the branches of the portal vein 

 and hepatic artery. These three structures — thejiepatic artery, the 

 portal vein, and the bile duct, which always occur together in the con- 

 necdve tissue which marks the point of separation of three or more 

 lobules — together constitute the portal canal (Fig. 196). From the 

 interlobular ducts short branches pass to the surfaces of the lobules. 



4 





mm^-Ji 





V.:.-,.. , ^ ^^ - -^ /,■■. ■ _' ■ , > -•: . J^.\-: ^^tV'--'' - ' ■ '■"■-:.'■"' ■'"■ " ■'"'■'.' ' ■ ' .-'i^y- ■-, ,'.\".V,'-;f.''.-* / 



■^te,- 





""'><i.;,-y' N:^''' ' 



''^H^y 



Fig. 197. — Part of Lobule of Human Liver, showing capillaries and anastomosing cords 

 of liver cells. X350. a, Liver cells; b, capillaries. 



From these are given off extremely narrow tubules, which enter the 

 lobule as intralobular secreting tubules. 



The walls of the ducts consist of a single layer of epithelial cells 

 resting upon a basement membrane and surrounded by connective 

 tissue (Fig. 196). The height of the epithelium and the amount of 

 connective tissue are directly proportionate to the size of the duct. 

 In the largest ducts there are usually a few scattered smooth muscle 

 cells. The walls of the secreting tubules are formed by the liver cells. 



The LIVER CELLS (Fig. 197) are irregularly polyhedral in shape. 

 They have a granular protoplasm which frequently contains gly- 



