108 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



But what has become of the hepatic artery? As soon as it has 

 entered the sheath, it gives off branches to the capsule forming 

 part of the vaginal plexus and entering into the vaginal branches 

 of the portal vein just before these run between the lobules. It 

 also furnishes branches to the wall of the portal vein, to the wall 

 of the larger divisions of the artery itself, and to the hepatic duct. 



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

 number of lobules about one-twenty-fifth of an inch in diameter, 

 separated by vessels, nerves and radicles of the hepatic duct. 

 Such a lobule in certain of the lower animals has a distinct poly- 

 gonal 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 intralobular 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 difficult to demonstrate the interlobu- 

 lar 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 carried 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 rela- 

 tion does not always hold good, every cell does communicate 

 with both kinds of capillaries. The interlobular bile ducts con- 

 sist of epithelium resting 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 



