THE LIVER 417 



longitudinal muscle fibers 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 laver. 



As has been pointed out by Mall ( 1 !><)<;) the hepatic lobule cannot be 

 regarded as the homologue of the lobule of other glands. For the portal 

 canal with its bile duel, the excretory duct of the glandular unit, should 

 be axial to the functional lobnlar unit. Moreover, an interlobular bile 

 duct drains not the whole of a particular lobule, but portions of a num- 

 ber of adjacent lobules. The functional unit (jtortal lobule], in contra- 

 distinction to the structural unit (hepatic lobule), is accordingly that 

 portion of liver tissue (portions of a number of hepatic lobules) sup- 

 plied by an ultimate branch of the vessels of a portal canal. Thus a 

 hepatic lobule is drained by several bile ducts, and conversely, a single 

 ultimate bile duct drains portions of several hepatic lobules. 



Blood Supply. The liver is supplied with blood from two inde- 

 pendent sources, the hepatic artery and the portal vein. That supplied 

 by the artery is of minor importance and is destined only for the nutri- 

 tion 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 Interlobular arteries, which ramify in the 

 tissue of Glissoirs 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 iutralobular capillaries which are derived from the branches of the 

 portal vein. 



THE PORTAL VEIN. The portal vein likewise enters at the transverse 

 fissure, bringing 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 reins, 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. These inlralnbular 

 capillaries (capilliform xhtuxuiilx, Lewis) converge toward the center of 

 the lobule and anastomose to form a capillary network, in the elongated 

 meshes of which are the cords of hepat ic cells. These capillaries approach 

 the center of the lobule where they unite to form the iutralobular or 



