330 THE LIVER 



than the interlobular arteries. The ducts are lined by columnar 

 epithelium whose height varies with the size of the tubule, the 

 smallest ducts being lined by low columnar or cuboidal, the largest 

 by tall columnar cells ; the lining epithelium of the hepatic and 

 common bile ducts is very tall. The epithelial cells of the ducts 

 possess characteristic spherical or ovoid nuclei which are heavily 

 loaded with chromatin. Their cytoplasm is clear or finely reticu- 

 lar. The largest ducts contain a few goblet cells ; small mucous 

 glands are found in the hepatic and common bile duct. 



The epithelium of the interlobular bile ducts rests upon a 

 thin basement membrane, which is surrounded by a thick fibro- 

 elastic coat. The larger ducts are also supplied with circular 

 smooth muscle fibres, which, in the largest branches, form a con- 

 siderable coat (Fig. 239, page 293). Outside of the liver longitu- 

 dinal muscle fibres also appear in the walls of the excretory ducts, 

 and so accumulate in the wall of the gall bladder and common 

 bile duct as often to form a distinct layer. 



BLOOD SUPPLY. The liver is supplied with blood from two 

 independent sources, the hepatic artery and the portal vein. That 

 supplied by the artery is of minor importance and is destined only 

 for the nutrition of the connective tissue framework of the organ. 



On entering the liver at the transverse fissure the hepatic 

 artery gives off numerous capsular branches which ramify in the 

 capsule of the liver and supply capillaries to its connective tissue. 

 Other branches, the direct continuation of the hepatic artery, 

 enter the portal canals and by repeated division form the inter- 

 lobular arteries, which ramify in the tissue of Glisson's capsule, 

 and whose vaginal branches supply capillaries to this connective 

 tissue. These capillaries, as well as those from the capsular 

 branches, become continuous, at the periphery of the lobule, with 

 the intralobular capillaries which are derived from the branches 

 of the portal vein. 



The Portal Vein likewise enters at the transverse fissure, bring- 

 ing to the liver the blood collected from the capillaries of the 

 organs of digestion and absorption. It divides into numerous 

 branches which follow the portal canals, in which they are known 

 as the interlobular veins, and in this way reach all portions of the 

 organ. 



The interlobular veins throughout all their course give off 

 small branches which at once enter the periphery of the hepatic 

 lobules and immediately break into a brush of capillary vessels. 



