DECIDUA REFLEXA. 751 



course. The tubules are about 0.05 millimetre in diameter, and are 

 lined with columnar epithelium. They occupy the entire thickness of 

 the uterine mucous membrane, their closed extremities resting upon 

 the subjacent muscular tissue, while their mouths open into the cavity 

 of the uterus. A few fine bloodvessels penetrate the mucous membrane 

 from below, and, running upward between the tubules, encircle their 

 superficial extremities with a capillary network. There is no connective 

 tissue in the uterine mucous membrane, but only a few isolated nuclei 

 and spindle-shaped fibre-cells, scattered between the tubules. 



Decidua Vera. As the fecundated egg descends through the Fal- 

 lopian tube, the uterine mucous membrane takes on an increased 

 activity of growth. It becomes tumefied and vascular ; and, as it in- 

 creases in thickness, it projects, in rounded eminences or folds, into 

 the uterine cavity. (Fig. 265.) In .this process the uterine tubules in- 

 crease in length, and also become wider ; so that their open mouths may 

 be readily seen by the naked eye upon the uterine surface, as numerous 

 minute perforations. According to the observations of Kolliker, so 

 early as the end of the first week they have increased to three or four 

 times their original length and width, so that they measure at this time 

 on the average nearly 0.20 millimetre in diameter, The bloodvessels of 

 the mucous membrane also enlarge and communicate freely with each 

 other ; the vascular network between and around the tubules becoming 

 more extensive and abundant. The internal surface of the uterus, after 

 this process has been for some time going on, presents a thick, rich, soft, 

 velvety, and vascular lining, quite different in appearance from that 

 which is to be found in the unimpregnated condition. It is now known 

 as the decidua ; and in order to distinguish it from a similar growth of 

 subsequent formation, it has received the special name of the decidua 

 vera. 



The production of the decidua is confined to the body of the uterus, 

 the mucous membrane of the cervix taking no part in the process, but 

 retaining its original appearance. The decidual membrane commences 

 above, at the orifices of the Fallopian tubes, and ceases below, at the 

 situation of the os intern um. The cavity of the cervix, meanwhile, is 

 filled with an abundant secretion of its peculiarly viscid mucus, which 

 blocks up its passage, and protects the internal cavity. If the uterus 

 be opened, therefore, in this condition, its internal surface will be seen 

 lined with the decidua vera, which is continuous, at the os internum, 

 with the unaltered mucous membrane of the cervix uteri. 



Decidua Reflexa. As the fecundated egg passes the lower orifice of 

 the Fallopian tube, it insinuates itself between the opposite surfaces of 

 the uterine mucous membrane, and becomes lodged in one of the furrows 

 or depressions between the folds of the decidua. (Fig. 265.) At this 

 situation an adhesion subsequently takes place between the external 

 membranes of the egg and the uterine decidua. At the point where 

 the egg thus becomes fixed, a still more rapid development takes place 

 in the uterine mucous membrane. Its projecting folds grow up around 



