CHAP. XXXIII.] PORTAL CANALS. 465 



an isolated and separate liver, and the whole gland as an agglo- 

 meration of smaller ones, connected by the penultimate branches 



Lobules of a cat's liver, partially injected through the portal vein, and also through the hepatic vein. 

 a. Twigs of portal vein. 6. Capillaries springing from them, which serve to mark the outline of the 

 lobules, d. Capillaries in the centre of the lobules injected from the hepatic vein. e. Situations at 

 which the injection forced into the two vessels has met. I. Central parts of lobule not injected. 



of the portal vein, artery and duct, which run between the 

 lobules, and by the areolar tissue which accompanies them ; but 

 not by any inosculation or coalescence of the ultimate secreting 

 elements, the liver-cells, or the capillaries. In other animals, 

 and in the human subject, the lobules are not thus isolated, but 

 are only imperfectly marked out by the several points of their 

 exterior, to which the ultimate twigs of the portal vein and duct 

 arrive. The twigs of the vein terminate in a plexus of capillaries 

 common to all the contiguous lobules, and continuous between them, 

 so that the lobules themselves have no definite limit (Fig. 219), 

 but blend with each other, except at certain points of their exterior. 

 It is not likely that these differences in the isolation of the lobules 

 in various animals are of any physiological importance, but they 

 have, probably, given rise to much of the difference of opinion 

 which exists among anatomists on this subject. 



The shape of the lobules, whether completely denned by an 

 investment of fibrous tissue, or merely mapped out by the position 



