FCETAL MEMBRANES. 



109 



mesoderm extends peripherally beyond the disk between the ectoderm and 

 entoderm (Fig. 89). It will be remembered also that the mesoderm later splits 

 into two layers— the parietal and visceral, of which the parietal plus the ecto- 

 derm forms the somatopleure and the visceral plus the entoderm forms the' 



~Embryoi/ic duK 

 Coelo 



Primitive fl/t 



Fig. 100. — Diagrams representing six stages in the development of the fcetal membranes 



in a mammal. Modified from Kolliker. 



The ectoderm is indicated by solid black lines; the entoderm by broken lines; the mesoderm 



by dotted lines and areas. 



splanchnopleure; and that the cleft between the two layers is the body cavity 

 or ccelom. 



In further development, along with the differentiation of the embryonic 

 body, the somatopleure begins to fold dorsally at a short distance from the 



