FORMATION OF THE DECIDUA. 



617 



mucous membrane. Its projecting folds begin to grow up around 

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

 circumvallation of the decidua, and to shut it off, more or less corn- 



Fig. 213. 



IMPREGNATED UTERCS; 

 formation of decidua. The decidua is 

 represented in black ; and the egg is 

 seen, at the fundus of the uterus, en- 

 paged between two of its projecting 

 convolutions. 



Fig. 220. 



IMPREGNATED UTERUS, with pro- 

 jecting 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 promi- 

 neut portion of the egg. 



Fiir. 221. 



pletely, from the general cavity of the uterus. (Fig. 220.) The egg 

 is thus soon contained in a special cavity of its own, which still 

 communicates for a time with the general cavity of the uterus by 

 a small opening, situated over its most 

 prominent portion, Avhich is known as the 

 " decidual umbilicus." As the above pro- 

 cess of growth goes on, this opening be- 

 comes narrower and narrower, while the 

 projecting folds of decidua approach each 

 other over the surface of the egg. At 

 last these folds actually 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 and 

 its contents has reached this point (Fig. 

 221), it will be seen that the egg is com- 

 pletely inclosed in a distinct cavity of its 



own ; being everywhere covered with a decidual layer of new for- 

 mation, which has thus gradually enveloped it, and by which it is 

 concealed from view when the uterine cavity is laid open. This 



UTERTS; 

 showing egg completely inclo-ed 

 by decidua reflexa. 



