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FCETAL MEMBRANES. 



FlG. 147. FIVE DIAGRAMMATIC FIGURES ILLUSTRATING THE FORMATION OF 

 THE FCETAL MEMBRANES OF A MAMMAL. (From Kolliker.) 



In i, 2, 3, 4 the embryo is represented in longitudinal section. 



1 . Ovum with zona pellucida, blastodermic vesicle, and embryonic area. 



2. Ovum with commencing formation of umbilical vesicle and amnion. 



3. Ovum with amnion about to close, and commencing allantois. 



4. Ovum with villous subzonal membrane, larger allantois, and mouth and anus. 



5. Ovum in which the mesoblast of the allantois has extended round the inner 



