THE LIVER 



407 



phragm (septum trans ver sum) and of the intervening ventral mesentery 

 throughout which the entodermal tubules ramify, and in part (the-retre- 

 ulum) from endothelium of the original venous sinusoids (Mall). 



The liver js dependent for its structural characteristics upon the 

 peculiar disposition of the connective tissue of Glisson's 

 of the blood-vessels whose, branches it contains; for by these tissues the 

 substance of the liver is ex- 

 tensively subdivided into mi- 

 nute collections of hepatic 

 cells, each group forming an 

 anatomic unit, the hepatic 

 lobule, which in addition to 

 the hepatic cells contains a 

 connective tissue reticulum 

 and the smaller blood-vessels 

 andjsecretory capillaries ( bile 

 canaliculi). 



The hejaatic^ lobules are 

 of cylindrical shape7"aT>out 2 

 millimeters in length and 1 

 millimeter in diameter (Bai- 

 ley). In transverse section 

 they present a polygonal 

 (hexagonal or pentagonal) 

 outline. In the dog they are 

 short polyhedra about 0.7 



millimeter high, and 0.7 millimeter in diameter; the entire liver con- 

 taining 480,000 (Mall, Amer. Jour. Anat., 5, 3, 1906), They are anal- 

 ogous to the lobules of compound tubulo-acinar glands, inasmuch as they 

 contain the secreting parenchyma of the organ, but are very different 

 from the latter in the arrangement of the secreting cells which, in the 

 human liver, do not present either a tubular or acinar structure, but 

 form solid cell columns. Thus in the human liver the tubular character 

 of the gland is scarcely apparent, yet in the liver of many of the lower 

 animals, notably in that of the turtle and frog, the cells form typical 

 tubules within the indistinct hepatic lobules. 



The bile^f ormed by the liver cells is conveyed to the duodenum by 

 an excretory system, beginning^trir-innUmerable interlobular bile due 

 which receive the intralobular secretory capillaries, and, leaving the 

 lobule "from all its sides, find their way through the interlobular con- 



FIG. 380. FROM A SECTION OF THE TURTLE'S 

 LIVER, SHOWING THE TUBULAR ARRANGE- 

 MENT OP THE PARENCHYMA. 



a, blood capillary, partially filled with clotted 

 blood; 6, vascular endothelium; c, darkened 

 central portions of the hepatic cells; d, periph- 

 eral portion of the hepatic cells. Osmium 

 tetroxid; carmin. X 400. (After Shore and 

 Jones.) 



