752 DEVELOPMENT OF THE DEC1DUAL MEMBRANE. 



the egg in such a manner as to partially inclose it in a kind of circum- 

 vallation, and to shut it off, mure or less completely, from the general 



Fig. 265. 



Fig-. 2(;. 



IMPREGNATED UTERUS; showingfor- 

 mation of decidua. The decidua is repre- 

 sented in black; and the egg is seen, at the 

 fundus of the uterus, engaged between two 

 of its projecting folds. 



IMPREGNATED UTERUS, with project- 

 ing folds of decidua growing up around the 

 egg. The narrow opening, where the edges 

 of the folds approach each other, is seen 

 over the most prominent portion of the egg. 



iif. 267. 



cavity of the uterus. (Fig. 266.) The egg thus comes to be contained 

 in a special cavity of its own, which still communicates for a time with 

 the general cavity of the uterus, by an opening situated over its most 



prominent portion. As the process of growth 

 goes on, this opening becomes narrower, while 

 the decidual folds approach each other OA^er 

 the surface of the egg. At last these folds 

 touch each other and unite, forming a kind of 

 cicatrix which remains for a certain time, to 

 mark the situation of the original opening. 



When the development of the uterus has 

 reached this point (Fig. 267), the egg is com- 

 pletely inclosed in a cavity of its own ; being 

 everywhere covered with a decidual layer of 

 new formation, which has gradually enveloped 

 it, and by which it is concealed from view 

 when the uterine cavity is laid open. This 

 newly-formed layer, enveloping the projecting 

 portion of the egg, is called the Decidua 

 reflexa ; because it is reflected over the egg from the general surface 

 of the uterine mucous membrane. The orifices of the uterine tubules, 

 in consequence of the manner in which the decidua reflexa is formed, 

 are to be seen not only on its external surface, or that which looks 

 toward the cavity of the uterus, but also on its internal surface, or that 

 which looks toward the egg. 



The decidua vera, therefore, is the original mucous membrane lining 

 the surface of the uterus. The decidua reflexa is a new formation, 

 which grows up around the egg and incloses it in a distinct cavity. 



IMPREGNA.TKD UTERUS; 

 showing the egg completely in- 

 closed by the decidua reflexa. 



