376 RICHARD E. SCAMMON 



TTT. DEVELOPMENT OF THE GALL BLADDER AND CYSTIC DUCT 



The gall bladder has been described in the first section of this 

 l)aper as arising as a median outpouching of the anterior wall 

 of the yolk-stalk immediately below the point where that struc- 

 ture becomes continuous with the floor of the fore gut. The ven- 

 tral zone of the lateral walls and the floor of this part of the gut 

 at this early stage are a part of the hepatic area and that part of 

 the anterior wall of the yolk-stalk from which the gall bladder 

 arises is later incorporated in the gut behind the liver as the yolk- 

 stalk becomes constricted antero-posteriorly. The time of appear- 

 ance of the anlage of the gall bladder is somewhat later than that 

 of the. liver as has been noted by Laguesse ('93) and Debeyra 

 ('()9). It seems possible, from these observations, to regard the 

 gall bladder in this form as derived from a secondary pouch 

 which is formed in the floor of the archenteron immediately behind 

 the liver pouch proper. If this interpretation be correct, an ante- 

 rior shifting of the gall bladder by which its opening reaches its 

 later position at the anterior end of the ductus choledochus in 

 front of the openings of the hepatic ducts is to be expected. Evi- 

 dences of such a shifting are not wanting. The early demarkation 

 of the gall bladder has already been described in the preceding 

 section, and has been seen to consist of the formation of dorsal 

 longitudinal grooves and a posterior and ventral vertical one 

 by which the gall bladder is cut off from the anterior wall of the 

 yolk-stalk behind and remains attached to the liver pouch above 

 by a transversely constricted neck which extends along its entire 

 dorsal surface. The anterior end of this neck is less constricted 

 and represents the cystic duct. These changes are illustrated in 

 figures 33, 35 and 37, and are also shown in B of figure 26 below. 



These changes are even more marked in an embryo of 10 mm. 

 illustrated in figures 39 and 40, and in C of figure 26. Along 

 with them is a considerable lateral expansion of the gall bladder 

 and a curious growth of its anterior wall which produces a pointed 

 [irocess which projects forward below the ventral wall of the me- 

 dian hepatic pouch. The gall bladder in this and the preceding 

 stages which follow its separation from the anterior wall of the 



