236 EXCRETION. 



its course it sends branches to the sheath (vaginal vessels), 

 which afterward go between the lobules. The distribution 

 of the hepatic artery, however, is not so simple. This vessel 

 has three sets of branches. As soon as it enters the sheath 

 with the other vessels, it sends off minute branches (vasa 

 vasorum), to the walls of the portal vein, the larger branches 

 of the artery itself, the walls of the hepatic veins, and a very 

 rich net-work of branches to the hepatic duct. When the 

 hepatic artery is completely injected, the walls of the hepatic 

 duct are seen almost covered with vessels. In its course, 

 the hepatic artery also sends branches to the capsule of 

 Glisson (capsular branches), which join with the branches 

 of the portal vein to form the so-called vaginal plexus. 

 From these vessels a few arterial branches are given off and 

 pass between the lobules. The hepatic artery cannot be 

 followed beyond the interlobular spaces. According to Kol- 

 liker and others, the terminal branches of the hepatic artery 

 do not open into the radicles of the hepatic veins, but into 

 small branches of the portal vein, within the capsule of 

 Glisson. 1 



The hepatic duct follows the general course of the portal 

 vein ; but its structure and relations are so important and 

 intricate that they will be described separately. 



Interlobular Vessels. Branches of the portal vein, com- 

 ing from the terminal ramifications as the vessel branches 

 within the capsule and the branches in the walls of the cap- 

 sule, are distributed between the lobules, constituting the 

 greatest part of the so-called interlobular plexus. These are 

 situated between the lobules and surround them ; each ves- 

 sel, however, giving off branches to two or three lobules, and 

 never to one alone. They do not anastomose, and conse- 

 quently do not constitute a true plexus. The diameter 

 of these interlobular vessels varies from I4 1 4o to ^-^ of an 

 inch. 2 In this distribution, the blood-vessels are followed 



1 KOLLIKER, Handbuch der Gewebelehre des Menscken, Leipzig, 1867, S. 443. 



2 KOLLIKER, op. cit. t 1867, S. 441. 



