THE DECIDUA 



355 



of the new cells into three layers, from which the different parts 

 of the body of a new being and the membranes which envelop 

 it, will develop. When the impregnated ovum reaches the uterus 

 it finds extensive preparations already made for its reception. 

 Instead of being washed away by menstrual fluid, it is deposited 

 in a soft bed of the thickened mucous lining of the uterus which 

 has developed an increased growth and new features for the 

 purpose. As this membrane will be discarded after the birth of 

 the child, it is called a true decidua, or decidua vera (Fig. 229.) 



The impregnated ovum becomes attached to the mucous 

 membrane usually near the fundus (see Fig. 230). This area of 



FIG. 229. THICK- 

 ENED LINING OF A 

 PREGNANT UTERUS. 



Showing decidua 

 vera, decidua serotina 

 and beginning of the 

 reflexa. (Dalton.) 



FIG. 230. THICKENED 

 LINING OF A PREGNANT 

 UTERUS. 



Showing decidua reflexa. 

 (Dalton.) 



fixation becomes the decidua serotina. A portion of the decidua 

 vera rises on every side of the ovum and thus forms a third decidua, 

 the decidua reflexa which finally encloses it. As the ovum grows 

 and the fetus develops to fill the uterine cavity, the decidua reflexa 

 becomes fused with the decidua vera and together they are dis- 

 charged in the lochia. The serotina becomes a part of the placenta. 



The decidua vera is the uterine decidua. 



The decidua reflexa is the ovular decidua. (Together these two 

 disappear in the lochia.) 



The decidua serotina is the placental decidua. 



