X.] 



THE HUMAN EMBRYO. 

 Fia. 110. 



337 



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Three Eaelt Human Embryos. (Copied from His.) 



A. Side view of an early embryo described by His. 



B. Embryo of about 12 — 14 days described by AUen Thom- 

 son. 



C. Young embryo described by His. 



am. amnion ; md. medullary groove ; wn. umbilical vesicle ; 

 ch. chorion, to which the embryo is attached by a stalk. 



and yolk-sac filled up but a very small part of the 

 whole cavity of the vesicle. 



The embryo, which was probably not quite normal 

 (Fig. 110 A), was very imperfectly developed; a me- 

 dullary plate was hardly indicated, and, though the 

 mesoblast was unsegmented, the head fold, separating 

 the embryo from the yolk-sac (wm), was already in- 

 F. & B. 22 



