THE LIVER 



249 



I 



anastomosis of the tubules, in part by the interrelation of the bile and 

 blood-vessels. 



With development the liver grows cephalad from its point of 

 origin, but this forward growth is limited by the presence of the 

 blood-vessels which develop the sinus venosus and the hepatic veins 

 and also contribute to the septum transversum (see circulation), and 

 so its later increase must cause it to grow in the opposite direction. 

 As it increases in size there is an immigration of mesenchyme be- 

 tween the lobules and with these the blood-vessels enter. At the 

 same time the liver grows away from the alimentary canal, carrying 

 the peritoneum before it so that it 

 receives an outer serous coat. 



Usually the bile duct (when there 

 are several ducts only one is con- 

 cerned) forms a lateral diverticulum, 

 the gall bladder, which serves as a 

 reservoir for the bile. This is 

 usually placed on the dorsal side of 

 the liver, but it may be immersed 

 in the substance of the gland. In 

 some cases, even in mammals, the 

 gall bladder may be lacking. When 

 a gall bladder is present, three re- 

 gions may be recognized in the bile Fig. 268— Diagrams of the develop- 

 , "^ 1 . 1 1 J /• ment of liver and pancreas, based on 



ducts. Those parts which lead from Schimkewitsch. dm, dorsal mesentery; 



the liver to the connexion with the '^^I J""^*^ pancreas; e ectoderm; en. 



^ entoderm; », intestme; /, liver; In, falci- 



bladder are called hepatic ducts; form ligament of liver; Ihd, hepato- 

 ,, i i_ xi 1^ J A duodenal ligament; *, peritoneum; vp, 



these are met by the cystic duct ventral pancreas. 



leading from the bladder, and the 



common duct, formed by the two and which empties into the intestine 

 is the choledochal duct (fig. 266). The shape of the gland is in part 

 determined by the shape of the body, being long in elongate species, 

 sometimes consisting of two consecutive lobes. Another modifying 

 factor is the shape and size of the adjacent organs, stomach, etc. 

 Usually the liver is divided into right and left halves, these correspond- 

 ing to the first division of the anlage, but these halves are hardly 

 indicated in some of the teleosts. Frequently, and especially in 

 mammals, the halves become subdivided into lobes of varying size, 

 which are arranged in various ways. The liver is relatively larger in the 

 ichthyopsida than in the amniotes, but the cyclostomes have a small 



