242 



EMBRYOLOGY. 



(blastula) no longer lies free in the cavity of the uterus, but is 

 enclosed in a special capsule produced by the growth of the mucous 

 membrane. Hitherto no one has had the opportunity to make 

 observations concerning the formation of this capsule. Following 

 an hypothesis of SHARPEY, which has been somewhat modified by 



Dv 



~g. 139. Diagrammatic section through the grwid human uterus, from WIEDEUSHEIM. 



U, Uterus ; UH, cavity of the same ; Tb, Fallopian tube ; DC, cecidua vera ; Dr, decidua reflexa, , 

 Pu, .placenta uterina (decidua serobiiia) ; Pf. placenta foe tails or choriou frondo3um (CUj) ', 

 Chi, chorion laeve ; A (on black background), cavity of the amnion filled with amniotie 

 fluid ; Z>, yolk- (umbilical) vesic'e ; in the embryo one sees the r.mbilical vessels (Al) ; t tho 

 livcjr traversed by the vera nmbilicalis ; //, the Jieavt ; A, the aorta; ci and cs, the vena 

 cava ii,ferior and superior ; p, vena pottaruui. 



KEICHERT, it is now generally assumed that the ovum upon its 

 entrance into the uterus imbeds itself in a depression of the mucous 

 membrane, which is thrown into ridges and is in process of being 

 metamorphosed into the decidua. The margins of the depression 

 soon grow around the blastula on all sides, and fuse together to form 

 a, closed foetal capsule. The fusion takes place at a point diametrically 



