616 DEVELOPMENT OF UTERINE MUCOUS MEMBRANE. 



each other ; so that the vascular network encircling the tubules be- 

 comes more extensive and abundant. 



The internal surface of the uterus, accordingly, after this process 

 has been for some time going on, presents a thick, rich, soft, vas- 

 cular, and velvety lining, quite different from that which is to be 

 found in the unimpregnated condition. In consequence of this 

 difference, the lining membrane of the uterus, in the impregnated 

 condition, was formerly supposed to be an entirely new product, 

 thrown out by exudation from the uterine surface, and analogous, 

 in this respect, to the inflammatory exudations of croup and pleu- 

 risy. It is now known, however, to be no other than the mucous 

 membrane of the uterus itself, thickened and hypertrophied to an 

 extraordinary degree, but still retaining all its natural connections 

 and its original anatomical structure. 



The hypertrophied mucous membrane, above described, consti- 

 tutes the Decidua vera. Its formation is confined altogether to the 

 body of the uterus, the mucous membrane of the cervix taking no 

 part in the process, but retaining its original appearance. The 

 decidua vera, therefore, commences above, at the orifices of the 

 Fallopian tubes, and ceases below, at the situation of the os inter- 

 num. The cavity of the cervix, meanwhile, begins to be filled 

 with an abundant secretion of its peculiarly viscid mucus, which 

 blocks up, more or less completely, its passage, and protects the 

 internal cavity. But there is no membranous partition at this time 

 covering the os internum, and the mucous membranes of the cervix 

 and of the body of the uterus, though very different in appearance, 

 are still perfectly continuous with each other. When we cut open 

 the cavity of the uterus, therefore, in this condition, we find its 

 internal surface lined with the decidua vera, with the opening of 

 the os internum below and the orifices of the Fallopian tubes above, 

 perfectly distinct, and in their natural positions. (Fig. 219.) 



As the fecundated egg, in its journey from above downward, 

 passes the lower orifice of the Fallopian tube, it insinuates itself 

 between the opposite surfaces of the uterine mucous membrane, 

 and becomes soon afterward lodged in one of the furrows or de- 

 pressions between the projecting convolutions of the decidua. 

 (Fig. 219.) It is at this situation that an adhesion subsequently 

 takes place between the external membranes of the egg, on the 

 one hand, and the uterine decidua on the other. Now, at the point 

 where the egg becomes fixed and entangled, as above stated, a still 

 more rapid development than before takes place in the uterine 



