158 NORMAL HISTOLOGY. 



cells often show depressions on their sides caused 

 by the pressure from adjacent blood-vessels. 



If we look at the cut surface of a fresh liver with 

 the naked eye, we find that it presents more or less 

 distinctly, small polygonal or irregular-shaped fig- 

 ures, which are. sections of certain groups of liver 

 cells, called acini or lobules. These lobules have, in 

 general, the form of oblong polyhedra, and the dif- 

 ference in shape presented by the sections is due to 

 the fact that they lie crowded together, with their 

 long axes lying in various directions. In order to 

 understand the structure of these lobules, it is neces- 

 sary to study them in connection with the blood- 

 vessels of the liver, to which they bear a very 

 constant and characteristic relation. 



The liver receives its blood from the portal vein 

 and the hepatic artery ; it is conveyed away by the 

 hepatic vein. If we follow the ramifications of the 

 hepatic vein, we find that it divides and subdivides 

 until it finally breaks up into short terminal radicles, 

 around which as a centre the oblong liver-lobules 

 are grouped. From its smaller branches also, before 

 it breaks up into terminal radicles, small, short 

 branchlets are given off, which form the centres of 

 lobules. Veins bearing this relation to the lobules 

 are called central veins or vena intralobulares. 



If now we follow the ramifications of the portal 

 vein, on the other hand, we find that, dividing and 

 subdividing, it, too, gives off small branchlets which, 



