324 



THE MAMMALIAN EMBRYO. 



[chap. 



ing medullary folds (Fig. 105 0, ae). Where this promi- 

 nence becomes first apparent the epiblast and hypoblast 



Fia. 105. 



A Series of Tkansvbese Sections thkouqh the Junction 

 OF THE Primitive Streak and Medullary Groove of 

 A Young Guinea-Pig. (After Sohafer.) 



A. is the posterior section. 



e. epiblast ; m. mesoblast ; h. hypoblast ; ae. axial epiblast of 

 the primitive streak ; ah. axial hypoblast attached in B. and 

 0. to the epiblast at the rudimentary blastopore ; ng. me- 

 dullary groove ; /. rudimentary blastopore. 



