ACTION OF THE FEMALE. 

 Fig. 249. Fig. 250. 



973 



Two thin segments of Human Dacidua, 

 after recent impregnation, viewed on a 

 dark ground ; they show the openings 

 on the surface of the membrane. A is 

 magnified six diameters and B twelve 

 diameters. At 1, the lining of epithelium 

 is seen within the orifices ; at 2, it has 

 escaped. From Dr. Sharpey (xxxii.). 



A portion of Fig. 248 more enlarged, show- 

 ing the convoluted extremities of the tubular 

 glandulae. 



978. The Deciduous membrane is found at a later period to consist of two 

 layers ; the Decidua vera lining the uterus, and the Decidua reflexa covering 

 the exterior of the ovum. Regarding the origin of this second layer, there has 

 been a good deal of difference of opinion. The doctrine first propounded by 

 Dr. W. Hunter, which is indicated by the name which he bestowed upon the 

 membrane, was that the decidua reflexa is a portion of the true decidua, which 

 has been pushed before the ovum at its entrance into the uterus; it being sup- 

 posed that the true decidua forms a completely closed sac (like that of a serous 

 membrane), against the outside of which the ovum is applied, so that it comes 

 to be invested by a double layer of it, as the heart is by the pericardium, or 

 the lungs by the pleura. But this view is negatived by a number of consider- 

 ations. For, in the first place, the original decidua does not form the closed 

 sac which this supposition involves, but extends (like the mucous membrane 

 of which it is a metamorphosed form) into the Fallopian tubes ; and the ovum, 

 at its entrance into the uterus, really lies upon its internal surface. But, 

 again, the texture of the two layers is 

 very different; for, as was first pointed 

 out by Prof. Goodsir (loc. cit.), the 

 decidua reflexa is almost entirely com- 

 posed of cells, exhibiting few or none 

 of the orifices of the glandular follicles 

 which are characteristic of the decidua 

 vera, except near the part where the 

 two layers are continuous. According 

 to the observations of M. Coste, how- 

 ever, there is a considerable resem- 

 blance between the two layers at an 



Fig. 251. 



First stage of the formation of the Decidua reflexa 

 around the ovum. 



early period: and he considers the 



following to be the mode in which the second investment is formed : When 



