EXCRETION. 



lobules is about one-quarter of the diameter of the lobule, 

 and is occupied with the blood-vessels, nerves, and ramifica- 

 tions of the hepatic duct, all enclosed in the fibrous sheath. 

 In a few animals, as, for example, the pig and the polar-bear, 

 the division of the hepatic substance can be readily made 

 out with the naked eye ; but in man and in most of the 

 mammalia, the lobules are not so distinct, though their ar- 

 rangement is essentially the same. Although the lobules 

 are intimately connected with each other from the fact that 

 branches going to a number of different lobules are given off 

 from the same interlobular vessels, they are sufficiently dis- 

 tinct to represent, each one, the general anatomy of the 

 secreting substance of the liver ; but before we study the 

 minute structure of the lobules, it will be convenient to fol- 

 low out the course of the vessels and the duct, after they 

 have penetrated at the transverse fissure. In this descrip- 

 tion we will follow, in the main, the observations of Iviernan, 

 who has given, probably, the most accurate account of the 

 vascular arrangement in the liver. 1 



At the transverse fissure, the portal vein, collecting the 

 blood from the abdominal organs, and the hepatic artery, a 

 branch of the coeliac axis, penetrate the substance of the 

 liver, with the hepatic duct, nerves, and lymphatics, all en- 

 veloped 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 calibre may be roughly estimated 

 at from 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 ves- 

 sels 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 



1 KIERXAK, The Anatomy and Physiology of the Liver. Philosophical Trans- 

 actions, London, 1833, p. 711, et seq. 



