THE LIVER. 



677 



endothelial walls, which are arranged in close contact, without a 

 marked caliber. This disposition of vessels is, as a matter of course, 

 less noticeable in injected specimens than in those taken from 

 livers which are simply hardened. From this fact we may infer that 

 the capillary system of the lobule is never completely filled with 

 blood j and if the blood-supply at one surface of an epithelium 

 is abundant, the capillary 

 at the opposite surface is 

 closed. It is also admissi- 

 ble to suppose that, by the 

 enlargement of a number of 

 epithelia, during their secre- 

 tory action, some capillaries 

 are occluded; or lastly, it 

 may be that new capillaries 

 are forming in the lobules 

 of the liver during the whole 

 life of the individual. 



The capillary meshes are 

 extremely narrow, so that 

 there is never room for more 

 than two complete epithelia 

 between two capillaries. We 

 often find, where the capil- 

 laries exhibit a radiating 

 arrangement, rows of epi- 

 thelia lying between them ; 

 and the appearance of these 

 epithelial rows is caused by the occlusion of transverse capillaries 

 which connect the longitudinal vessels. The transverse capillaries 

 in such cases can be recognized by their endothelia with high 

 powers of the microscope only. As a rule, therefore, one half of 

 the epithelial circumference will be supplied with blood, although 

 a greater portion may be encircled by capillaries. (See Fig. 297.) 



The center of a lobule holds the hepatic vein, which arises as an 

 abrupt widening from the confluence of the capillaries. It is 

 surrounded by a very small amount of connective tissue, has no 

 muscle coat, and is never accompanied by bile-ducts or arteries. 

 The hepatic veins, which always occupy the centers of the lobules, 

 unite into somewhat larger branches, which are most marked 

 on the posterior portion of the liver, and are called sublobular 

 veins. By the union of these the hepatic veins proper originate. 



FIG. 297. LIVER OF A CHILD. 



C, capillary blood-vessels, partly gaping, partly 

 occluded, holding in their meshes the liver epithe' 

 lia ; B, bile-capillary (1), cut transversely. Mag- 

 nified 500 diameters. 



