338 



SECRETION. 



Fig. 108. 



the portal system. The blood which has circulated through the 

 capillaries of the stomach, spleen, pancreas, and intestine is col- 

 lected by the roots of the corresponding veins, and discharged into 

 the portal vein, which enters the liver at the great transverse 

 fissure of the organ. Immediately upon its entrance, the portal 

 vein divides into two branches, right and left, which supply the 

 corresponding portions of the liver; and these branches success- 

 ively subdivide into smaller twigs and ramifications, until they are 

 reduced to the size, according to Kolliker, of 1^-^ of an inch in 

 diameter. These veins, with their terminal branches, are arranged 

 in such a manner as to include between them pentagonal or 

 hexagonal spaces, or portions of the hepatic substance, -J$ to ylj 

 of an inch in diameter in the human subject, which can readily be 

 distinguished by the naked eye, both on the exterior of the organ 

 and by the inspection of cut surfaces. The portions of hepatic 

 substance included in this way between the terminal branches 



of the portal vein (Fig. 108) 

 are termed the "acini" or 

 "lobules" of the liver; and 

 the terminal venous branches, 

 occupying the spaces between 

 the adjacent lobules, are the 

 "interlobular" veins. In the 

 spaces between the lobules 

 we also find the minute 

 branches of the hepatic ar- 

 tery, and the commencing 

 rootlets of the hepatic ducts. 

 As the portal vein, the he- 

 patic artery, and the hepatic 

 duct enter the liver at the 

 transverse fissure, they are 

 closely invested by a fibrous 



sheath, termed Glisson's capsule, which accompanies them in their 

 divisions and ramifications. In some of the lower animals, as in the 

 pig, this sheath extends even to the interlobular spaces, inclosing 

 each lobule in a thin fibrous investment, by which it is distinctly 

 separated from the neighboring parts. In the human subject, how- 

 ever, Glisson's capsule becomes gradually thinner as it penetrates 

 the liver, and disappears altogether before reaching the interlobular 

 spaces ; so that here the lobules are nearly in contact with each 



Ranrfication of PORTAL VEIN IN LIVER. a. 

 Twig of portal vein. 6,6. I uteri obular veins, c. Aciui. 



