DEVELOPMENT OF THE AMNION. 



659 



retires toward the vitelline membrane, with which it unites to 

 form the primitive chorion. 



The true amnion,then, is a sack formed of an outer layer derived 

 from the inesoblast and an inner layer derived from the epiblast. 



FIG. 253 B. 



rt, 





e. Embryo, a. Amnion. a'. Alimentary canal, vt. Vitelline membrane, of. Amniotic 

 fold. ae. Amniotic cavity, y. Yelk. al. Allantois. 



The false amnion likewise consists of mesoblast and epiblast, but 

 here the epiblast is external. The true amnion is continuous with 

 the skin of the embryo, and when the foetus is mature, the con- 



