78 



THE SECOND DAY. 



[chap. 



for some little time their line of junction (Fig. 23). 

 The open medullary groove of the first day has thus 

 become converted into a tube, the neural canal, closed 

 in front, but as yet open behind. Even before the 



Fig. 27. 



Embryo of the Chick between thirty and thirty-six hours, 



VIEWED FROM ABOVE AS AN OpAQUE ObJECT. 



(Chromic acid preparation.) 



/.6"f front- brain : mb. mid-brain ; h.h. hind-brain ; op.v. optic vesi- 

 cle ; au.p. auditory pit ; o.f. vitelline vein ; p.v. mesoblastic 

 somite ; m.f. line of junction of the medullary folds above the 



