DIGESTIVE ORGANS. 



233 



The bile is passed to the intestine by the bile duct (choledochal or 

 hepatic duct), but the other products are carried away by the blood 

 (internal secretion). 



Theanlage of the liver is a ventral diverticulum from the archenteron 

 (p. 206), which grows forward from its point of origin, branches again 

 and again, the ultimate branches forming the glandular part of the 

 organ, the proximal parts of the outgrowth giving rise to the bile duct 

 (ocasionally multiple) which empties into the intestine. As a result of 

 this method of formation the liver is to be regarded as a compound 

 tubular gland, the lumens of the tubules forming the gall capillaries 

 which eventually empty into the duct. This tubular condition is 

 readily recognized in the ichthyopsida, but it is masked in the amniotes 

 and especially in the mammals, in part by the 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 contrib- 

 ute to the septum transversum (hepatic 

 veins see circulation), and so its later 

 increase must cause it to grow in the op- 

 posite direction. As it increases in size 

 there is an immigration of mesenchyme 

 between the lobules and with these the 



FIG. 240. FIG. 241. 



FIG. 240. Diagram of two types of bile ducts, b, gall bladder; ch, choledochar duct; 

 h, hepatic ducts; i, intestine. 



FIG. 241. Liver and pancreas of American ostrich (Rhea) after Gegenbaur. d, duo- 

 denum; dh, bile ducts;/, liver; oe, oesophagus ;p, pancreas; pd, pancreatic duct; s, stomach. 



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 



