VI.] 



THE TAIL-FOLD. 

 FiQ. 59. 



171 



B. 



Transverse Sections through a Chick Embryo with 



TWENTT-ONE MeSOBLASTIC SoMITES TO SHEW THE FOR- 

 MATION OP THE Pericardial Cavity, A. being the 



ANTERIOR section. 



jyp. body cavity ; pc. pericardial cavity ; al. alimentary cavity ; 

 au. auricle ; v. ventricle ; sm. sinus venosus ; do. ductus 

 Cuvieri ; ao. aorta ; mp. muscle-plate ; mc. medullary cord. 



The alimentary canal. As we stated above, the 

 folding in of the splanchnopleure to form the alimentary 

 canal is proceeding w^ith great rapidity, the tail-fold as 

 well as the head-fold contributing largely to this result. 



The formation of the tail-fold is very similar to that 

 of the head-fold. The tail is a solid, somewhat curved, 

 blunt cone of mesoblast, immediately coated with the 



