VI.] 



THE TAIL-FOLD. 

 FIG. 59. 



171 



B. 



TRANSVERSE SECTIONS THROUGH A CHICK EMBRYO WITH 

 TWENTY-ONE MESOBLASTIC SOMITES TO SHEW THE FOR- 

 MATION OF THE PERICARDIAL CAVITY, A. BEING THE 



ANTERIOR SECTION. 



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

 au. auricle ; v. ventricle ; sv. sinus venosus ; dc. ductu& 

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



The alimentary canal. As we stated above, the 

 folding in of the splanchnopleure to form the alimentary 

 canal is proceeding 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 



