342 



THE ANATOMY OF THE HORSE. 



examined, it shows a system of lines mapping it out into areas about 

 the size of a pin's head. These areas are sections of the lobules of the 

 liver which are united together by interlobular connective-tissue. As 

 the liver of the horse contains very little interlobular connective-tissue 

 the outlines of the lobules are not very distinct ; but the interlobular 

 connective tissue is much more abundantly developed in the pig, and, 

 consequently, in that animal the lobulation of the liver substance is 



much more evident. A lobule 

 may be viewed as having a 

 frame -work of blood-vessels, 

 in which are set the liver- 

 cells. Between the adjacent 

 cells the rootlets of the bile 

 passages begin, and there are 

 also branches of nerves and 

 lymphatic vessels. 



The liver is supplied with 

 blood by two vessels. The 

 first and much the larger of 

 the two is the portal vein, the 

 other is the hepatic artery. 



The Portal Vein collects 

 its blood from the stomach, 

 intestines, spleen, and pan- 

 creas. Entering the liver at 

 the portal fissure, this vein 

 comports itself like an artery, 

 in that it reduces itself by 

 division and subdivision to 

 branches, that become pro- 

 gressively smaller until they 

 terminate in a set of capil- 

 laries. In their course through 

 the liver, the larger branches 

 of the vein run in tunnels of the liver substance — the portal canals 

 — which also contain branches of the hepatic artery and bile ducts, 

 surrounded by connective- tissue (Glisson's capsule). The ultimate 

 small branches of the portal vein are distributed in the interlobular 

 connective-tissue, where, at the circumference of each lobule, they form 

 an interlobular plexus. From this plexus capillary vessels penetrate 

 the lobule, and form within it the intralobular plexus. The capillaries 

 of this last plexus converge towards the axis of the lobule, and there 

 empty themselves into what is termed the central vein of the lobule. 

 This is the initial vessel of the hepatic system of veins, and at the base 



Fig. 46. 



Longitudinal Section of a Portal Canal, con- 

 taining a Portal Vein, Hepatic Artery, and 

 Hepatic Duct from the Pig (after Kiernan). 

 About 5 Diameters. 



P. Branch of vena portse, situated in a portal 

 canal, formed amongst the hepatic lobules of the 

 liver ; p. p. Larger branches of portal vein, giving 

 off smaller ones (i. i.), named interlobular veins ; 

 there are also seen within the large portal vein 

 numerous orifices of interlobular r veins arising 

 directly from it ; a. Hepatic artery ; d, Biliary 

 duct. 



