lOO 



EARLY EMBRYOLOGY OF THE CHICK 



or the neural plate. These cells form a pair of longitudinal 

 aggregations extending one on either side of the mid-dorsal 

 line in the angles between the superficial ectoderm and the 

 neural tube (Fig. 37, A). With the fusion of the edges of the 

 neural folds to complete the neural tube, and the fusion of the 

 superficial ectoderm dorsal to the neural tube, these two longi- 

 tudinal cell masses become for a time confluent in the mid-line 



neural crests 



superficial 



ectoderm 



Pig. 37. — Drawings from transverse sections to show origin of neural crest 

 cells. The location of the area drawn is indicated on the small sketch to the 

 left of each drawing. 



A, anterior rhombencephalic region of 30-hour chick; B, posterior rhomb- 

 encephalic region of 36-hour chick; C, mid-dorsal region of cord in 5 5-hour 

 chick. 



(Fig. 37, B). But because this aggregation of cells arises from 

 paired components and soon again separates into right and left 

 parts it is to be considered as potentially paired. On account 

 of its position dorsal to the neural tube it is known as the neural 

 crest. 



The neural crest should not be confused with the margin of 



