678 THE LIVER. 



The term " interlobular veins " is used to designate the portal 

 branches lying between the lobules, and the term " intralobular 

 veins n the central hepatic veins. These denominations are, how- 

 ever, superfluous and easily confounded. 



The rows of the liver epithelia, as mentioned before, may be 

 either single or double i. e., there may be a capillary blood- 

 vessel on either side of the epithelium, or the epithelia may lie 

 close together in one capillary mesh. In places where the capillaries 

 run in a prevailing longitudinal direction, this relation is not well 

 marked, as the epithelia overlap the capillaries on all sides ; while, 

 in places (see Fig. 299) where the capillaries are cut transversely, 

 their relation to the epithelia these being arranged wreath-like 

 around the blood-vessel is plain. (See Fig. 300.) Some authors 

 claim that there is never more than one epithelium in a capillary 

 mesh ; if this were true, the small openings at the corners of 

 neighboring epithelia (marked B in Fig. 297) would have to be 

 considered transverse sections of very narrow or occluded capil- 

 laries, and not bile-capillaries. In the human liver it is impos- 

 sible to decide in every instance whether a minute transverse 

 section in the middle of an epithelial group is a narrow capillary 

 blood-vessel or a bile-capillary. Much confusion has been caused, 

 especially in the description of morbid processes, by the inability 

 of positively discriminating between the two above-named forma- 

 tions. Those who claim that the bile-capillaries have an 

 endothelial investment certainly must have mistaken capillary 

 blood-vessels for them. 



The liver epithelia form a continuous layer around the capil- 

 lary blood-vessels, although in thin sections their continuity 

 appears interrupted by the calibers of the capillaries. In the 

 human liver the single epithelia are cuboidal, irregularly polyhe- 

 dral ; in the rabbit's liver, more or less hexagonal. They exhibit 

 one or two nuclei ; the latter condition being rarer in the human 

 than in the rabbit's liver. In the nuclei, as well as in the body of 

 the epithelia, the reticular bioplasson structure is visible, as seen 

 in all living elements of the tissues, including the epithelial. 

 The liver epithelia are separated from each other by a light, nar- 

 row rim of cement-substance which is traversed at right angles 

 by extremely delicate filaments, identical with the so-called 

 " thorns" or " prickles" met with in other epithelial formations. 

 These features were discovered in my laboratory by H. Chr. Miil- 

 ler. The bile-capillaries are simply excavations in the cement- 

 substance. (See Fig. 298.) 



