322 



THE MAMMALIAN EMBRYO. [CHAP. 



Fia. 103. 



EMBRYONIC AREA OF A SEVEN DAYS' EMBRYO RABBIT. 

 (From Kolliker.) 



o. place of future area vasculosa ; rf. medullary groove ; pr. pri- 

 mitive streak ; ag. embryonic area. 



In the region o. a layer of mesoblast has already grown ; there 

 are however as yet no signs of blood-vessels in it. 



This mesoblast is derived from the mesoblast of the primitive 

 streak (Kolliker). 



in the axial line with the primitive hypoblast. When 

 the medullary groove is formed the lateral bands of 

 raesoblast become separate from the axial hypoblast and 

 give rise to two independent lateral plates of mesoblast 



