DISCHARGE OF FCETUS AND PLACENTA. 765 



The cord also contains, for a certain period, the pedicle or stem of 

 the umbilical vesicle. The situation of this vesicle, necessarily, is 

 always between the chorion and the amnion. Its pedicle gradually 

 elongates with the growth of the umbilical cord ; and the vesicle itself, 

 which generally disappears soon after the third month,, sometimes re- 

 mains as late as the fifth, sixth, or seventh. According to Mayer, it 

 may even be found, by careful search, at the termination of pregnancy. 

 In the middle and latter periods of gestation, it presents itself as a 

 small, flattened vesicle, situated beneath the amnion, at a variable dis- 

 tance from the insertion of the umbilical cord. A minute bloodvessel 

 is often seen running to it from the cord, and ramifying upon its 

 surface. 



The decidua reflexa, during the latter months of pregnancy, is con- 

 stantly distended by the increasing size of the egg, and finally pressed 

 against the opposite surface of the decidua vera. By the end of the 

 seventh month, the decidua vera and reflexa are in contact, though still 

 distinct and capable of being easily separated. After that time, they 

 become confounded with each other, forming at last only a single, thin, 

 friable, semi-opaque layer, in which no trace of glandular structure can 

 be discovered. 



This is the condition of things at the termination of pregnancy. 

 Then, the time having arrived for parturition to take place, the hyper- 

 trophied muscular walls of the uterus contract upon its contents, and 

 the egg is discharged, together with the decidual membrane. 



In the human species, as well as in most quadrupeds, the membranes 

 of the egg are usually ruptured during the process of parturition ; and 

 the foetus escapes first, the placenta and the rest of the appendages fol- 

 lowing a few moments afterward. Occasionally the egg is discharged 

 entire, and the foetus afterward liberated by the laceration of the mem- 

 branes. In each case the mode of separation and expulsion is essen- 

 tially the same. 



The process of parturition, therefore, consists in a separation of the 

 decidual membrane, which, on being discharged, brings away the ovum 

 with it. The greater part of the decidua. vera, having fallen into a 

 state of atrophy during the latter months of pregnancy, is by this time 

 nearly destitute of vessels, and separates without perceptible hemor- 

 rhage. That portion which enters into the formation of the placenta is, 

 on the contrary, excessively vascular; and when the placenta is sepa- 

 rated, and its maternal vessels torn off at their insertion, a gush of 

 blood takes place, which accompanies or immediately follows the birth 

 of the foetus. This hemorrhage, which occurs at the'time of parturition, 

 does not come immediately from the uterine vessels. It consists of 

 blood which was contained in the placental sinuses, and which is ex- 

 pelled from them owing to the compression of the placenta by the 

 muscular walls of the uterus. Since the whole amount of blood thus 

 lost was previously employed in the placental circulation, and since the 

 placenta itself is thrown off at the same time, no unpleasant effect is- 



