42 PRELIMINARY ACCOUNT. [CHAP. IT. 



it lies, or else replaces it, and in the later days of incuba- 

 tion is known as the chorion. 



In the above account we have described the somatopleure as consisting 

 of mesoblast as well as epiblast even in its most peripheral portions. The inner 

 limbs of the amniotic folds undoubtedly contain mesoblastic elements, since 

 the amnion proper contains plain muscular fibres. Some authors however 

 regard the outer limbs of the amniotic folds (giving rise to the false amnion) 

 and the somatopleure beyond them as being composed of epiblast only. 



