VI.J 



THE TAIL-FOLD. 

 Pig. 59. 



171 



B. 



Tkansversb Sections through a Chick Embryo with 

 Twenty-one Mesoblastic Somites to shew the For- 

 mation OF THE PeRICAEDIAX CaVITY, A. BEINO THE 



anterior section. 



pp. body cavity ; po. pericardial cavity ; al. alimentary cavity ; 

 au. auricle ; v. ventricle ; sv. sinus venoaus ; do. ductus 

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



The alimentary canal. As we stated above, the 

 folding in of the splanchnopleure to form the alimentary 

 canal is proceediag with 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 



