618 DEVELOPMENT OF UTERINE MUCOUS MEMBRANE. 



newly -formed layer of decidua, enveloping, as above described, the 

 projecting portion of the egg, is called the Decidua reflexa ; because 

 it is reflected over the egg, by a continuous growth from the general 

 surface of the uterine mucous membrane. The orifices of the uterine 

 tubules, accordingly, in consequence of the manner in which the 

 decidua reflexa is formed, will be seen not only on its external sur- 

 face, or that which looks toward the cavity of the uterus, but also on 

 its internal surface, or that which looks toward the egg. 



The decidua vera, therefore, is the original mucous membrane 

 lining the surface of the uterus ; while the decidua reflexa is a new 

 formation, which has grown up round the egg and inclosed it in a 

 distinct cavity. 



If abortion occur at this time, the mucous membrane of the 

 uterus, that is, the decidua vera, is thrown off, and of course brings 

 away with it the egg and decidua reflexa. On examining the mass 

 discharged in such an abortion, the egg will accordingly be found 

 imbedded in the substance of the decidual membrane. One side 

 of this membrane, where it has been torn away from its attachment 

 to the uterine walls, is ragged and shaggy ; the other side, corres- 

 ponding to the cavity of the uterus, is smooth or gently convoluted, 

 and presents very distinctly the orifices of the uterine tubules; 

 while the egg itself can only be extracted by cutting through the 

 decidual membrane, either from one side or the other, and opening 

 in this way the special cavity in which it has been inclosed. 



During the formation of the decidua reflexa, the entire egg, as 

 well as the body of the uterus which contains it, has considerably 

 enlarged. That portion of the uterine mucous membrane situated 

 immediately underneath the egg, and to which the egg first became 

 attached, has also continued to increase in thickness and vascularity. 

 The remainder of the decidua vera, however, ceases to grow as 

 rapidly as before, and no longer keeps pace with the increasing 

 size of the egg and of the uterus. It is still very thick and vascu- 

 lar at the end of the third month ; but after that period it becomes 

 comparatively thinner and less glandular in appearance, while the 

 unusual activity of growth and development is concentrated in the 

 egg, and in that portion of the uterine mucous membrane which is 

 in immediate contact with it. 



Let us now see in what manner the egg becomes attached to the 

 decidual membrane, so as to derive from it the requisite supply of 

 nutritious material. It must be recollected that, while the above 

 changes have been taking place in the walls of the uterus, the 



