MEMBRANE DECIDUA. 907 



becomes the. urinary bladder ; but there is a temporary communication between the inter- 

 nal portion and the lower portion of the cord, which is called the urachus. This is gen- 

 erally obliterated before birth and is reduced to the condition of an impervious cord ; 

 but it may persist during the whole of intra-uterine life, in the form of a narrow canal, 

 extending from the bladder to the umbilicus, which is closed soon after birth. 



Meiribrance Deciduce. In addition to the two membranes connected with the foetus, 

 there are two membranes formed from the mucous membrane of the uterus, which are 

 derived from the mother and which serve still farther to protect the ovum. The cho- 

 rion, as we have just seen, is for the protection of the foetus ; but a portion of this 

 membrane, about one-third of its surface, becomes closely united with a corresponding 

 portion of the uterine mucous membrane, to form the placenta. This organ, which 

 serves for the nutrition of the fcetus, will be described by itself ; but, before we can 

 thoroughly comprehend its structure and the process of its development, we must study 

 carefully the formation of the membranae deciduse. 



As the fecundated ovum descends into the uterus, it is usually invested with a shaggy 

 covering, which is either the permanent chorion or one of the membranes which invests 

 the ovum previous to the complete development of the allantois. At this time, the 

 mucous membrane of the uterus has undergone certain changes by which it is prepared 

 for the reception of the ovum. The changes which this membrane undergoes in men- 

 struation have already been studied. It has been seen that, during an ordinary men- 

 strual period, the membrane has been increased three or four times in thickness and has 

 become more or less rugous. Without being able to state from positive observation the 

 character of the first changes in the uterine mucous membrane preceding the descent of 

 the fecundated ovum for the opportunities for direct inspection of these parts after 

 fecundation and before the arrival of the ovum are not frequent it is almost certain 

 that this hypertrophy occurs and progresses. One of the most favorable occasions for 

 observing these early changes in the human subject lately presented itself, and the ap- 

 pearances were minutely described by Reichert. In this case, the ovum was lenticular, 

 measuring nearly one-fourth of an inch in its long and about one-sixth of an inch in 

 its short diameter. It was covered with simple, empty, cylindrical villi, and was esti- 

 mated to be at from the twelfth to the thirteenth day of its development, dating from 

 fecundation. It was enclosed in the decidua reflexa, and it was thought that this 

 had been accomplished from twenty-four to forty-eight hours before the death of the 

 mother. 



According to Reichert, the thickening of the mucous membrane of the uterus which 

 occurs at each menstrual period, in case the ovum be not fecundated, is relieved by a flow 

 of blood and disappears ; but, if fecundation take place, the membrane continues to hyper- 

 trophy and to prepare itself to enclose the ovum. In this process, when an ovum has 

 been fecundated, there are formed, upon the surface of the mucous membrane, little ele- 

 vations, or islands, provided with primary and secondary papillae everywhere except at 

 their borders, where the membrane is smooth and presents the enlarged orifices of the 

 uterine follicles. The ovum observed by Reichert was found embedded in the parenchyma 

 of one of these islands ; and, as it was detached, several villi were drawn immediately out 

 from the uterine tubules. 



It is now well known that the mucous membrane lining the gravid uterus forms what 

 has been called the decidua vera, and that a portion is reflected over the ovum, to form 

 the decidua reflexa. Reichert is of the opinion that the view entertained by most ob- 

 servers, that the fecundated ovum lodges itself in one of the furrows of the hypertrophied 

 membrane and is finally enclosed by an elevation of the walls of the furrow, cannot be 

 sustained. He thinks that the ovum first becomes attached to one of the " islands; " at 

 the point of attachment, the island does not increase in size as rapidly as at other por- 

 tions, so that the ovum rests in a cup-shaped depression ; and, finally, a growth takes place 



