DECIDUA 69 



By the sixth week degenerative changes show themselves. The glandular 

 epithelium in the stratum spongiosum begins to be shed in places ; and, soon 

 after, the surface epithelium is thrown off, until in the fourth month all traces 

 of it have disappeared. 



After the fourth month, by which time the great increase in size of the chorionic 

 vesicle with its contained embryo has brought the decidua capsularis into close 

 contact with the decidua vera, the latter begins to undergo an atrophic process, 

 the result to all appearance of the compression and distension to which it is thus 

 subjected. Its tissue becomes thinner and less vascular, and both the funnel- 

 shaped mouths of the glands and those parts of the glands which run through 

 the stratum compactum become gradually obliterated, so that eventually hardly 

 any trace remains. In the stratum spongiosum the spaces which have resulted 

 from the dilatation of the gland-tubes lose their lining epithelium, and become 

 flattened out conformably to the surface, so that they now appear as a layer of 

 compressed lacunae, separated by thin fibrous trabeculae. 



Decidua capsularis (reflexa). It has already been shown that the decidua 

 capsularis is not formed, as used to be supposed, by an upgrowth of folds round 

 the ovum, but is originally that part of the mucous membrane in which the ovum 

 has excavated a cavity for its lodgment. As the ovum imbeds itself in the stratum 

 compactum alone, it follows that the decidua capsularis represents only the super- 

 ficial part of the mucous membrane, and therefore has not a stratum spongiosum 

 properly so called. Over the ovum there is at first an area in which there is little 

 or no decidual tissue, the capsule being completed by a fibrinous lamella formed by 

 the organisation of the blood-clot at the point of entrance. This constitutes 

 Reickert's scar, which used to be considered as the point of fusion of the folds of the 

 reflexa. The inner aspect of the capsularis is irregular ; it is not covered with 

 epithelium, nor do any gland-mouths open into the decidual cavity. 



The decidua capsularis resembles at first in every essential respect that portion 

 of the excavation which lies next the uterine wall and which becomes the decidua 

 basalis. The inter-relations between the mucous membrane and the villi are at first 

 similar all round the ovum. As the growing ovum expands, however, the decidua 

 capsularis and the villi imbedded in it degenerate (fig. 97). A gradual process of 

 atrophy supervenes until the membrane is reduced to a thin fibrinous or hyaline 

 lamella in which all traces of glands and vessels have disappeared. By the third 

 month the capsularis has nearly everywhere come into contact with the decidua vera 

 so as to obliterate the cavity of the uterus. In the advanced months of pregnancy 

 it wholly disappears, so that the chorion comes to lie directly against the decidua 

 vera. The degenerative process at work in the membrane does not seem to be 

 a fatty degeneration, as long held, but a coagulation necrosis. 



Decidua basalis (serotina). The decidua basalis is that portion of the 

 mucous membrane which intervenes between the blastocyst and the uterine wall, 

 opposite the original point of entrance of the ovum (fig. 93). The deeper portions 

 of the gland-tubes proper to it become much dilated, the final result being the 

 formation of a spongy layer, with irregular clefts flattened out conformably to the 

 surface, and from which the epithelium has entirely disappeared. At the same 

 time all the parts of the glands which are superficial to this layer suffer complete 

 atrophy, the only portions which remain nearly unaltered being the deepest parts 

 of the tubes, which are partly imbedded in the muscular coat of the uterus, and 

 retain their epithelium. After separation of the placenta from the uterine wall 

 at parturition, the uterine mucous membrane, with its epithelium and glands, 

 becomes renewed from this deepest portion of the decidua basalis. The blood- 

 capillaries become much dilated into sinus-like vessels, and the interglandular 

 tissue becomes crowded with decidual cells, derived, as in the decidua vera, from the 



