CH. XXXITT.] 



CIRCULATION IN THE LIVER 



505 



through the substance of the liver, they are contained in small channels 

 called portal canals, their immediate investment being a sheath of 

 areolar tissue continuous with G-lisson's capsule. 



To take the distribution of the portal vein first : In its course 

 through the liver this vessel gives off small branches which divide 

 and subdivide between the lobules surrounding them and limiting 

 them, and from this circumstance called inter-lobul&r veins. From 

 these vessels a dense capillary network is prolonged into the substance 

 of the lobule, and this network converges to a single small vein, 

 occupying the centre of the lobule, and hence called mra-lobular. 

 This arrangement is well seen in fig. 404, 

 which represents a section of a small piece 

 of an injected liver. 



The small m?*a-lobular veins discharge 

 their contents into veins called s^6-lobular 

 (h h h, fig. 405) ; while these, again, by their 

 union, form the main branches of the hepatic 

 veins, which leave the posterior border of 

 the liver to end by two or three principal 

 trunks in the inferior vena cava, just before 

 its passage through the diaphragm. The 

 sul-lobular and hepatic veins, unlike the 

 portal vein and its companions, have little 

 or no areolar tissue around them, and their 

 coats are very thin. 



The hepatic artery, the chief function of 

 which is to distribute blood for nutrition 

 to G-lisson's capsule, the walls of the ducts 

 and blood-vessels, and other parts of the 

 liver, is distributed in a very similar manner 

 to the portal vein, its blood being returned 

 by small branches which pass into the capillary plexus of the lobules 

 which connects the inter- and mtfra-lobular veins. 



The hepatic duct divides and subdivides in a manner very like that 

 of the portal vein and hepatic artery, the larger branches being lined 

 by columnar, and the smaller by small polygonal epithelium. 



The bile-capillaries commence between the hepatic cells, and are 

 bounded by a delicate membranous wall of their own. They are 

 always bounded by hepatic cells on all sides, and are thus separated 

 from the nearest blood-capillary by at least the breadth of one cell 

 (figs. 406 and 407). 



To demonstrate the intercellular network of bile capillaries, 

 Chrzonszezewsky employed a method of natural injection. A 

 saturated aqueous solution of sulph-indigotate of soda is introduced 

 into the circulation of dogs and pigs by the jugular vein. 



FIG. 406. Portion of a lobule of 

 liver, a, bile capillaries be- 

 tween liver-cells, the network 

 in which is well seen ; b, blood 

 capillaries, x 350. (Klein 

 .and Noble Smith.) 



The 



