9S 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 
Fig. 52.— The same embryo from beneath. 
a.ec. v., Amnio-eardiac vesicle. 
Sl the ad-fold. r’a., Proamnion. 
H. F., Head-fold. Pr’ P 
a. i. p., Anterior intestinal portal. 
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, ete.,) meeting, by the time four or five somites are 
