518 STRUCTURAL ANATOMY OP THE LIVER. 



thirds of its cylinder, the opposite 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 

 lobular. The vaginal branches are those which, being given off in 

 the portal canals, have to pass through the sheath (vagina) of Glis- 

 son's capsule, previously to entering the interlobular spaces. In 

 this course they form an intricate plexus, the vaginal plexus, which, 

 depending for its existence 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 interlo- 

 bular 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 spaces and 

 divide into branches, which cover with their ramifications every 

 part of the surface of the lobules with the exception of their bases, 

 and those extremities of the superficial lobules which appear upon 

 the surfaces of the liver. The interlobular veins communicate 

 freely with each other, and with the corresponding veins of adjoin- 

 ing fissures, and establish a general portal anastomosis throughout 

 the entire liver. The lobular branches are derived from the interlo- 

 bular veins ; they form a plexus within each lobule, and converge 

 from the circumference towards the centre, where they terminate 

 in the minute radicles of the intralobular portal vein. This plexus, 

 interposed between the interlobular portal veins and the intralobular 

 hepatic vein, constitutes the venous part of the lobule, and may be 

 called the lobular venous plexus. The irregular islets of the substance 

 of the lobules, seen between the meshes of this plexus by means of 

 the microscope, are the acini of Malpighi, and are shown by Mr. 

 Kiernan to be portions of the lobular biliary plexus. 



The portal vein returns the venous blood from the chylopoietic 

 viscera, to be circulated through the lobules ; it also receives the 

 venous blood which results from the distribution of the hepatic artery. 



The Hepatic duct, entering the liver at the transverse fissure, 

 divides into branches, which ramify through the portal canals, with 

 the portal vein and hepatic artery, to terminate in the substance of 

 the lobules. Its branches, like those of the portal vein, are vaginal, 

 interlobular, and lobular. 



The Vaginal branches ramify through the capsule of Glisson, and 

 form a vaginal biliary plexus, which, like the vaginal portal plexus, 

 surrounds the vessels in the large canals, but is deficient on that side 

 of the smaller canals near which the duct is placed. The branches 

 given off by the vaginal biliary plexus are interlobular and lobular. 



