IO8 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



forming part of the vaginal plexus and entering into the vag- 

 inal branches of the portal vein just before these run be- 

 tween the lobules. It also furnishes branches to the wall of 

 the portal vein, to the wall of the larger divisions of the ar- 

 tery itself, and to the hepatic duct. 



Histology of a Lobule. The liver is made up of a large 

 number of lobules about one-t wenty-.fi fth of an inch in di- 

 ameter, separated by vessels, nerves and radicles of the he- 

 patic duct. Such a lobule in certain of the lower animals has 

 a distinct polygonal shape, but in man the outlines are not 

 clear. In the lobule are the hepatic cells, ovoid in shape, 

 possessed of small granules and one or two nuclei. They 

 are disposed in columns radiating from the central intralob- 

 ular vein. These cells belong to the epithelial type, and the 

 liver is not essentially different from other glands, such as 

 the salivary, except in the complexity of its arrangement. 

 The analogy is established by the origin of the bile ducts in 

 the lobules between the cells. 



Bile Ducts. It is not difficcult to demonstrate the inter- 

 lobular ducts, but to follow them as such into the lobule is 

 less easy. However, there is no doubt at all that they do 

 originate between the hepatic cells. It is probable that here 

 they have no distinct lining membrane, but are mere tubular 

 intercellular spaces, into which the bile is poured and car- 

 ried into the interlobular duct. Typically a liver cell has 

 one of these bile capillaries on one side and a blood capillary 

 on the other, and while this relation does not always hold 

 good, every cell does communicate with both kinds of capil- 

 laries. The interlobular bile ducts consist of epithelium rest- 

 ing upon a very thin basement membrane. As they increase 

 in size they gain fibrous inelastic and elastic tissue, and the 

 largest, some non-striated muscular elements. Gradually as 

 the ducts become larger the lining epithelium changes from 

 the columnar to the pavement form. Mucous glands exist in 

 the largest ducts. The interlobular ducts join each other and 

 gradually increase in size as they merge from all parts of the 



