CHAP, vi.] THE CAT'S ALIMENTARY SYSTEM. 



187 



d a 



The cystic duct is convoluted, making about four turns, held 

 together by areolar tissue. 



The several hepatic ducts correspond with the different lobes 

 of the liver, and are formed by the union of small ducts arisin" 

 from the several ^ liver (or hepatic) lobes. The ductus communis 

 choledochus sensibly enlarges 

 as it traverses the coats of the 

 duodenum. 



The MINUTE STliUCTUllE of 



the liver consists of a com- 

 plex arrangement of microscopic 

 blood-vessels and cells, con- 

 nected by areolar tissue, as 

 follows : 



When the substance of the 

 liver is cut across, its solid sub- 

 stance presents a mottled ap- 

 pearance, and careful inspection 

 shows that it is made up of a 

 number of polygonal masses, 

 which are called lobules. These 

 lobules are seen to be arranged 

 around a number of canals pro- 

 ceeding in two directions. One 

 set of canals diverge from the 

 portal fissure, and these are 

 called portal canals. The other 

 set of canals converge to the 

 inferior vena cava, and these 

 are called hepatic veins. Now, 

 as will be hereafter seen, the 

 blood is of two kinds, arterial 

 and venous, and is respectively 

 conveyed (except as regards the 

 lungs,) by vessels called arteries 

 and veins, accordingly as they 

 carry the one or the other kind 

 of blood. No less than three sets of vessels ramify in the substance of 

 the liver, two sets conveying blood into, and one set (the hepatic veins) 

 conveying blood out of it. Of the two sets of vessels conveying blood 

 into it, one is arterial, the hepatic artery, the other is venous, the portal 

 vein. These ramify in the portal canals along with branches of the 

 hepatic ducts, the whole three sets of ramifications being surrounded 

 and supported by areolar tissue, which is continuous with a fibrous 

 membrane which invests the external surface of the liver generally. 

 The several branches of the portal vein are much larger than the 

 accompanying hepatic ducts, and these are somewhat larger than 

 the arteries. The arteries convey nutriment to the framework 

 of the liver ; its branches ending in the walls of the ducts, blood- 



Fig. 98. LONGITUDINAL SECTION OF A PORTAL 

 CANAL, CONTAINING A PORTAL VEIN, HEPATIC 

 ARTERY, AND HEPATIC DUCT, FROM THE PIG. 

 ENLARGED ABOUT FIVE DIAMETERS. 



P. Branch of vena portfe, situated in a portal 

 canal, formed amongst the hepatic lobules 

 of the liver. 



pp. Larger branches of the portal vein, giving 

 oft' smaller ones (i i), named inter-lobular 

 veins ; there are also seen within the larg; 

 portal vein numerous orifices of iuter- 

 lobular veins arising directly from it. 



a. Hepatic artery. 



d. Biliary duct. 



At c c, the venous wall has been partially 

 removed. 



