SEC. 1. THE STRUCTURE OF THE LIVER. 



445. The liver is a gland, the conducting portion of which, 

 the bile-duct or gall-duct, after repeated division ends in passages 

 lined by secreting structures ; but the comparatively simple 

 arrangement seen in other glands in which the terminal ducts or 

 ductules end in blind, tubular or flask shaped alveoli is, in the 

 liver, modified and to a certain extent obscured. These modi- 

 fications may be ascribed on the one hand to the fact that the 

 cells which provide the secretion, being also engaged as we have 

 just said in important metabolic duties, are developed out of 

 proportion to the biliary passages, and on the other hand to the 

 fact that the ordinary vascular supply of an artery (hepatic 

 artery) ending through capillaries in a vein (hepatic vein), is 

 overshadowed by the great portal system ; the great and wide 

 vena portas divides into venous capillaries, and these are gathered 

 up again into the hepatic vein, which thus draws its main supply 

 of blood from it rather than from the much smaller hepatic artery. 



The whole liver, invested with a capsule of connective tissue 

 and marked out into its several lobes, is divided by septa of con- 

 nective tissue into a number of small primary units of somewhat 

 polygonal form, called lobules, each being in mass about the size 

 of a pin's head. The distinctness of a lobule from its neighbours 

 depends on the relative abundance of the connective tissue which 

 separates them ; and this is much more conspicuous in some animals 

 (such as the pig) than in others (such as the rabbit or man). 



The large portal vein, the much smaller bile-duct and the 

 still smaller hepatic artery, entering the liver together on its 

 under surface at the porta hepatica, or gate of the liver, are in- 

 vested with a considerable quantity of connective tissue, carrying 

 also lymphatics and nerves, which is continuous with the connective 

 tissue covering of the whole liver and is called Glisson's capsule. 

 Rapidly dividing, the divisions continuing to run together side by 

 side in the beds of connective tissue into which Glisson's capsule 

 is continued, the three vessels ultimately reach the outsides of the 

 several lobules, the septa of connective tissue defining the lobules 



F. 45 



