DEVELOPMENT OF THE ELASMOBRANCH LIVER 



377 



yolk-stalk behind lies a little to the left of the median line. This 

 asymmetric position has already been discussed in Part I. It is 

 associated with the rotation of the gut in connection with the 

 formation of the spiral valve. 



WTien the liver reaches the stage represented in figures 41 

 and 42, of an embryo of 15 mm., the gall bladder is so far sepa- 

 rated from it as to form a thick walled ovoid sac, the posterior 

 half of which is rounded and free and the anterior end drawn 

 out into a cone shaped projection. It is still broadly attached 



Fig. 26 A series of semi-schematic figures of the development of the gall bladder 

 and cystic duct. A, embryo of 7 mm. ; B, embryo of 7.5 mm. ; C, embryo of 10 mm. ; 

 D, Embryo of 15.5 mm. ; E, embryo of 19 mm. ; F, embryo of 20.6 mm. ; G, embryo 

 of 33.1 mm. All from plastic reconstructions with the exception of .4, which 

 is based upon longi-sections. D.choL, ductus choledochus; D.cyst., cystic duct; 

 D.hep., hepatic dyct; G.bl., gall bladder; Hep.d., hepatic diverticulum. 



to the median liver pouch above. The posterior end extends 

 downward so that the long axis of the sac is no longer parallel 

 with that of the median liver pouch above it. 



The gall bladder in an embryo of 15.5 mm. (figs. 45 and 46 and 

 D, fig. 26) is smaller relatively, and the connection between it 

 and the liver above is drawn out into a short broad stalk, the 

 cystic duct. The pointed anterior extremity is less noticeable 

 than in the two preceding specimens and from this time on no 

 evidences are seen of it. In this specimen, also, the gall bladder 



