X.] 



THE HUMAN EMBRYO. 

 Fm. 110. 



337 



ch-- 



um 



Three Early Human Embryos. (Copied from His.) 



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



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

 son. 



C. Young embryo described by His. 



am. amnion ; md. medullary groove ; um. 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 (urn), was already in- 

 F. & B. 22 



