STRUCTURAL ANATOMY OF THE LIVER. 521 



each lobule a distinct capsule, which invests it on all sides with the ex- 

 ception of its base, connects all the lobules together, and constitutes the 

 proper capsule of the entire organ. But Glisson's capsule is not mere 

 areolar tissue ; " it is to the liver what the pia mater is to the brain ; it is a 

 cellulo-vascular membrane, in which the vessels divide and subdivide to 

 an extreme degree of minuteness ; which lines the portal canals, forming 

 sheaths for the larger vessels contained in them, and a web m which 

 the smaller vessels ramify ; which enters the interlobular fissures, and with 

 the vessels forms the capsules of the lobules ; and which finally enters the 

 lobules, and with the blood-vessels expands itself over the secreting biliary 

 ducts." Hence arises a natural division of the capsule into three portions, 

 a v ginal, an interlobular, and a lobular portion. 



The vaginal portion is that which invests the hepatic artery, hepatic 

 duct, and portal vein, in the portal canals ; in the larger canals it com- 

 pletely surrounds these vessels, but in the smaller is situated only on that 

 side which is occupied by the artery and duct. The interlobular portion 

 occupies the interlobular fissures and spaces, and the lobular portion forms 

 the supporting tissue to the substance of the lobules. 



The Portal vein, entering the liver at the transverse fissure, ramifies 

 through its structure in canals, which resemble, by their surfaces, the ex- 

 ternal superficies of the liver, and are formed by the capsular surfaces of 

 the lobules. These are the portal canals, and contain, besides the portal 

 vein with its ramifications, the artery and duct with their branches. 



In the larger canals, the vessels are separated from the parietes by a 

 web of Glisson's capsule ; but, in the smaller, the portal vein is in contact 

 with the surface of the canal for about two-thirds of its cylinder, the oppo- 

 site third being in relation with the artery and duct and their investing 

 capsule. If, therefore, the portal vein were laid open by a longitudinal 

 incision in one of these smaller canals, the coats being transparent, the 

 outline of the lobules, bounded by their interlobular fissures, would be as 

 distinctly seen -as upon the external surface of the liver, and the smaller 

 venous branches would be observed entering the interlobular spaces. 



The branches of the portal vein 



are, the vaginal, interlobular, and Fig. 231 -* 



lobular. The vaginal branches 

 are those which, being given off 

 in the portal canals, have to pass 

 through the sheath (vagina) of 

 Glisson's capsule, previously to 

 entering the interlobular spaces. 

 In this course they form an intri- 

 cate plexus, the vaginal plexus* 

 which, depending for it/exist- 

 ence on the capsule of Glisson, 

 necessarily surrounds the vessels, 

 as does that capsule in the larger canals, and occupies the capsular side 

 only in the smaller canals. The interlobular branches are given off from 

 the vaginal portal plexus where it exists, and directly from the portal 

 veins, in that part of the smaller canals where the coats of the vein are in 

 contact with the walls of the canal. They then enter the interlobular 



* Horizontal section of two superficial lobules, showing interlobular plexus of biliary 

 ducts. (JTieman.) 



44* 



