vi PEEGNANCY PAETUEITION PUEEPEEIUM 217 



fertilised ovum which has reached the morula stage has grafted 

 itself successfully in the thickness of this mucosa. In these cases 

 the menstrual decidua does not 4 



degenerate, but is transformed 

 into the decidua gravidica by 

 a process of further develop- 

 ment. Diagram 80 gives a fair 

 idea of the changes undergone 

 by the thickness of the uterine 

 mucosa as a whole and in each 

 of its layers. 



In the part in which the 

 ovum is grafted the mucosa 

 grows rapidly and forms a cap- 

 sule-like covering round the 

 ovum which, resembling a 

 mucous polyp, projects into the 

 cavity of the uterus (Fig. 81). 

 At this stage the part on which 

 the ovum is grafted is called the 

 basal decidua or decidua sero- 

 tina; that which enfolds the 

 ovum is termed the capsular or 

 decidua reflexa\ all the rest of 

 the mucosa of the uterine cavity 

 being called the decidua vera or 

 parietalis. The basal decidua 

 is interposed between the ovum 

 and the muscular tissue of the 

 uterus ; and since it is destined 

 to form the maternal portion 

 of the placenta, it is also called 

 the decidua placentalis. 



At the end of the second 

 month of pregnancy the ovum 

 is almost the size of a hen's 

 egg, and there is a space of from 



1 tO 2 Cm. between the parietal FIG. 80. Schematic sections of uterine mucosa 



and the reflex decidua. The 

 reflex decidua becomes steadily 

 thinner, while the parietal and 

 the placental become more 

 hypertrophic. 



During the following months 

 of gestation, the progressive increase in volume of the ovum 

 causes retrogressive processes in the uterine mucosa, and a 

 gradual approach of the decidua reflexa to the decidua vera, 



showing the changes undergone by the glands 

 when the mucosa is transformed into the 

 decidua of pregnancy. (Kundrat and Engel- 

 manu.) A, mucosa of non-gravid uterus ; m., 

 tunica muscularis. B, decidua parietalis at 

 beginning of pregnancy ; c., stratum com- 

 pactum ; sp., superficial part of stratum spongi- 

 osum ; d., deep part of stratum spongiosum ; 

 7H., tunica muscularis of uterus. 



