PHYSIOLOGICAL ANATOMY OF THE LIVER. 393 



nected with each other, and branches going to a number of different lobules 

 are given off from the same interlobular vessels ; but they are sufficiently 

 distinct to represent, each one, the general anatomy of the secreting portion 

 of the liver. 



At the transverse fissure, the portal vein, collecting the blood from the 

 abdominal organs, and the hepatic artery, which is a branch of the cceliac 

 axis, penetrate the substance of the liver, with the hepatic duct, nerves and 

 lymphatics, all enveloped in the fibrous vagina, or sheath, known as the cap- 

 sule of Glisson. The portal vein is by far the larger of the two blood-vessels, 

 and its caliber may be roughly estimated as eight to ten times that of the 

 artery. 



The vagina, or capsule of Glisson, is composed of fibrous tissue in the 

 form of a dense membrane, closely adherent to the adjacent structure of the 

 liver, and enveloping the vessels and nerves, to which it is attached by a loose, 

 areolar tissue. The attachment of the blood-vessels to the sheath is so loose 

 that the branches of the portal vein are collapsed when not filled with blood ; 

 presenting a striking contrast to the hepatic veins, which are closely adher- 

 ent to the substance of the liver and remain open when they are cut across. 

 This sheath is prolonged over the vessels as they branch and it follows them 

 in their subdivisions. It varies considerably in thickness in different animals. 

 In man and in the mammalia generally, it is rather thin, becoming more and 

 more delicate as the vessels subdivide, and it is entirely lost before the ves- 

 sels are distributed between the lobules. 



The vessels distributed in the liver are the following : 



The portal vein, the hepatic artery and the hepatic duct, passing in at 

 the transverse fissure, to be distributed in the lobules. The blood-vessels 

 are continuous in the lobules with the radicles of the hepatic veins. The 

 duct is to be followed to its branches of origin in the lobules. 



The hepatic veins ; vessels that originate in the lobules, and collect the 

 blood distributed in their substance by branches of the portal vein and of the 

 hepatic artery. 



Branches of the Portal Vein, the Hepatic Artery and the Hepatic Duct. 

 These vessels follow out the branches of the capsule of Glisson, become 

 smaller and smaller, and they finally pass directly between the lobules. In 

 their course, however, they send off lateral branches to the sheath, forming 

 the so-called vaginal plexus. The arrangement of the vessels in the sheath is 

 not in the form of a true anastomosing plexus, although branches pass from 

 this so-called vaginal plexus between the lobules. These vessels do not anas- 

 tomose or communicate with each other in the sheath. 



The portal vein does not present any important peculiarity in its course 

 from the transverse fissure to the interlobular spaces. It subdivides, enclosed 

 in its sheath, until its small branches go directly between the lobules, and in 

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

 go between the lobules. The hepatic artery 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, to the larger 



