136 THE ALIMENTARY SYSTEM. 



The hepatic artery is a small vessel, the branches of which 

 accompany those of the portal vein in the portal tracts. It 

 supplies blood for the nourishment of the connective tissue 

 and vessels of the liver. 



The bile-ducts collect and convey the bile from the secreting 

 lobules to the hepatic duct, the general outlet-duct of the liver. 

 They lie in the portal tracts. The smaller ducts are lined 

 with simple columnar epithelium (by which they may be dis- 

 tinguished from the accompanying arteries of corresponding 

 size), resting on a basement-membrane. As the ducts unite 

 and become larger the connective tissue by which they are 

 surrounded forms a thicker layer, in which elastic elements 

 and involuntary muscle-cells appear. 



The portal vein is the main afferent bloodvessel of the 

 liver, conveying into it the venous blood from the digestive 

 organs. Its branches follow the portal tracts, and are the 

 largest and thinnest- walled of the vessels in the latter. As its 

 branches lie always in the septa between the lobules, they are 

 called the interlobular veins. They divide into capillaries, 

 which penetrate and converge to the interior of the lobules, 

 and there empty into the radicles of the hepatic vein. 



The hepatic veins are the efferent bloodvessels of the liver. 

 They begin by the blind hepatic radicles or intralobular veins, 

 which lie in the centre or axis of the lobules and receive the 

 intralobular capillaries. The intralobular veins empty into 

 larger branches, the sublobular veins, the union of which forms 

 the hepatic veins. 



The lobules or acini of the liver are polyhedral in shape 

 from mutual pressure, and about a millimetre in diameter. 

 They are separated from one another by the interlobular septa 

 of the sustentacular tissue, though in man these septa are 

 incomplete and the boundaries of individual acini often diffi- 

 cult to determine. In cirrhosis of the liver and in some mam- 

 mals the septa are complete and well marked. 



Each lobule is made up of liver-cells, intralobular capilla- 

 ries, bile-passages between the cells, and an intralobular 

 vein in the centre or axis of the lobule. The acini are built 

 around the intralobular veins as axes, and their bases abut on 

 the sublobular veins into which these veins empty. 



The liver-cells are polyhedral, nucleated, glandular epithe- 



