322 



THE MAMJIALIAN EMBRYO. 

 Fia. 103. 



[chap. 



Embryonic Area or a Seven Days' Embryo Rabbit. 

 (From KoUiker.) 



0. place of future area vasoulosa ; rf. medullary groove ; pr. pri- 

 mitive streak ; ag. embryonic area. 



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

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



This mesoblast is derived from the mesoblast of the primitive 

 streak (KoUiker). 



iu the axial line with the primitive hypoblast. When 

 the medullary groove is formed the lateral bands of 

 mesoblast become separate from the axial hypobhist and 

 give rise to two independent lateral plates of mesoblast 



