292 



THE DIGESTIVE ORGANS. 



its contents into the bile capillary through a small tubule connect- 

 ing the vacuole with the bile capillary (Kupffer, 73, 89). 



The bile capillaries are, as we have remarked, nothing but tubu- 

 lar, capillary spaces between the hepatic cells, with no distinct indi- 

 vidual walls, although the outer portions of the liver cells (exc- 

 plasm) are somewhat denser than the remainder of the cells, 

 and serve to form a wall for the bile -capillaries. They may be 

 compared to the lumen of a tubular gland, although in the 

 human liver their walls consist of only two rows of hepatic 

 cells. In the lower vertebrates the walls of the bile capillaries 

 appear in transverse section to consist of several cells (in the 

 frog generally three, in the viper as many as five). The bile 

 capillaries naturally follow the course of the hepatic cords i. e., 

 in man extending radially. They form networks, the meshes of 

 which correspond to the size of the hepatic cells. At the periphery 

 of the lobule the hepatic cells pass directly over into the epithelial 

 cells of the smaller interlobular bile-ducts. The epithelium of the 

 latter is of the cubical variety, its cells being considerably smaller than 

 the hepatic cells. At the point 



where the hepatic cells become ^/ t _x\ ^-\ Bile capillaries, 

 continuous with the walls of the 

 smaller passages we find a few 

 cells of gradually decreasing size 

 which represent a transition stage 

 from the cells of the bile capil- 



Fig. 231. Schematic diagram of he- 

 patic cord in transverse section. At the 

 left the bile capillary is formed by four cells, 

 at the right by two ; the latter type occurs 

 in the human adult. 



Fig. 232. From the human liver, 

 showing the beginning of the bile-ducts ; 

 X 90 (chrome-silver). 



laries (hepatic cells) to those of the interlobular bile passages. 



The vascular system of the ' liver is peculiar in that, besides 

 the usual arterial and venous vessels common to all organs, 

 there is found another large afferent vein the portal vein. It 

 arises from a confluence of the 'superior and inferior mesenteric, 

 the splenic, coronary veins from the stomach, and cystic veins. 

 It divides into two branches, the right supplying the right lobe of 

 the liver, the left the remaining lobes. These branches again divide 

 into numerous smaller branches, the smallest of which finally reach 

 the individual lobules. Along its whole course through the inter- 



