98 



THE DEVELOPMENT OF THE CHICK 



anterior end of the plate (Fig. 48) (the neural groove) ; the mar- 

 gins of the anterior portion of the medullary plate then become 

 elevated somewhat above the surrounding blastoderm, forming 





MM mm 



mm 







■J 



■Si 





'U 





1 ( 



i 



Fig. 52. — The same embryo from beneath. 



a. c. v., Amnio-cardiac vesicle, a. i. p., Anterior intestinal portal. 

 H. F., Head-fold. Pr'a., Proamnion. 



the neural folds (Figs. 51 and 56). The latter rise very rapidly, 

 thus deepening the neural groove, and bend in towards the middle 

 line (Figs. 53,54, etc.,) meeting, by the time four or five somites are 



