DEVELOPMENT OF LIVER AND PANCREAS 217 



ing the constriction of the lateral walls of the gut. These veins 

 unite anteriorly and form the ductus venosus. The liver-anlage 

 therefore first grows ventrally and then anteriorly below the 

 horseshoe-shaped union of the omphalo-mesenteric veins and 

 the ductus venosus. A similar sagittal section of a later stage 

 shows the liver at the cranial end of a short ductus hepaticus 

 which is continuous caudally with the ductus choledochus. From 

 the ventral wall of the ductus choledochus there is now a very 

 marked outpouching, the gall-bladder, which is united with the 

 common duct by a short cystic duct. The primitive liver-an- 

 lage has thus grown cranialward and become separated from 

 the gut. Choronskitkzy believes this process to be due to the 

 growth and differentiation of the gut. The walls of the primi- 

 tive liver-anlage have folded and these folds later develop into 

 solid liver-columns. The liver grows around the developing 

 ductus venosus even to its dorsal surface and in so doing produces 

 many folds and columns which grow" through the ductus venosus 

 and divide it into sinus-like branches. 



Renter ('00) in his studies on the development of the intestine 

 of the Alytes obstetricans made mention of the early origin of 

 the liver. This develops from the 'Anfangsdarm' division of 

 the midgut. In later embryos the liver develops very rapidly 

 and is divided into three lobes. 



Gianelli ('01 and '02) described the hepatic anlage in Triton 

 as developing in two parts, the anterior giving rise to the he- 

 patic tissue proper and the caudal forming the hepatic duct. 

 The gall-bladder arises from a mass of cells belonging to the 

 primitive hepatic outpouching. By the development of the 

 intestinal folds the hepatic duct becomes attached to the dorsal 

 side of the gut. 



Weber ('03) stated that the observations made on the develop- 

 ment of the liver in the frog and in Triton differ but little. In 

 the latter the intimate relation of the anterior end of the hepatic 

 outpouching and the blood-vessels account for the develop- 

 ment of this part into the hepatic tissue proper. 



Bates ('04) in a paper on the histology of the digestive tract of 

 Amblystoma has described the hepatic and pancreatic ducts. 



