DEVELOPMENT OF LIVER AND PANCREAS 239 



a definite fold is shown between this and the ventrally extending 

 lumen of the hepatic anlage. Greil ('05) showed the gall-bladder 

 in a Bombinator embryo of 7 mm. length caudal to the hepatic 

 tissue but more closely connected with the liver than with the 

 yolk-mass behind it. In an embryo approximately- 7 mm. 

 long, which is undoubtedly an earlier stage in Amblystoma 

 (fig. 3) there is no distinct fold between the gall-bladder and- 

 liver-anlage. Only a slight median depression of the floor at 

 the posterior end of the hepatic diverticulum is present. No 

 difference is shown by ordinary stains in the epithelium lining 

 this early cystic evagination and that of the liver. Not until 

 later does the epithelium change into the low cuboidal type 

 characteristic of the adult gall-bladder. 



A little later the depression in the floor of the hepatic divertic- 

 ulum is considerably increased (fig. 36). The position of the 

 gall-bladder with reference to the opening of the hepatic anlage 

 has not changed. In a model of liver and gall-bladder of a 

 9 mm. embryo (fig. 37) the evagination is quite deep. There is 

 a distinct lateral constriction of the dorsal opening of the gall- 

 bladder and distinct anterior and posterior lips to the evagi- 

 nation, indicating the formation of a cystic duct (fig. 4) . There 

 is also a deep furrow anterior to the evagination separating the 

 gall-bladder from the hepatic anlage. The posterior furrow is 

 even more marked. The gall-bladder is, however, still very wide 

 laterally. 



In another embryo approximately 9 mm. long the gall-bladder 

 has a long cranio-caudal diameter. The furrow marking off 

 the gall-bladder from the hepatic tissue laterally is distinct. 

 The cystic duct is short and of large diameter and it, as well as 

 the gall-bladder, lies to the right of the midline. The cystic 

 duct projects upward and to the left (fig. 21). 



A section of the gall-bladder of an embryo 11.5 nmi. long 

 shows there has been a continual shifting to the right (fig. 6). 

 The cystic duct has become longer but is still of wide diameter. 

 It projects more to the left and upward. The gall-bladder, 

 though embedded between hepatic tissue and caudal yolk-mass, 

 is completely separated from both (fig. 22). In figure 23 is 



