134 



THE ALIMENTARY SYSTEM. 



on by intimate contact with the liver-cells before being again 

 collected in the hepatic vein and discharged into the general 

 circulation. 



In its passage through the liver the constituents of the 

 blood are, in ways not well understood, altered by the action 

 of the liver-cells for purposes useful to the animal econ- 

 omy. This action on the blood, of which the glycogenic 

 and urea-forming functions are known instances, partakes of 

 the nature of " internal " secretion. The liver also serves as 

 a storehouse for certain substances. As a gland the liver is of 

 the compound tubular type ; but in mammalia it is constructed 

 more with reference to its functions bearing on the blood, and 

 its glandular structure is masked and obscure. 



General structure : The liver consists of masses of epithelial 

 cells divided into small lobules or acini, supported in susten- 

 tacular tissue, and contains a network of outlet bile-ducts and 



FIG. 56. 



Lobules qf liver of pig, showing interlobular septa and a portal tract (Klein). 



three systems of bloodvessels : the hepatic artery, portal vein, 

 and hepatic vein ; besides scanty lymphatics and nerves. 



The sustentacular or connective tissue of the liver consists 

 of the capsule (of Glisson), interlobular septa, and the " portal 

 tracts." 



The capsule of Glisson is a fibrous envelope investing the 

 liver, beneath the peritoneum. The interlobular septa 



are 



