DISCHARGE OF THE FCETUS AND PLACENTA. 663 



sometimes remains as late as the fifth, sixth, or seventh. According 

 to Mayer, it may even be found, by careful search, at the termination 

 of pregnancy. When present in the middle and latter periods of ges- 

 tation, it is a small, flattened sac, situated beneath the amnion, on the 

 free surface of the placenta, at a variable distance from the insertion 

 of the umbilical cord. A minute blood-vessel is often seen running to 

 it from the cord, and ramifying upon its surface. 



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

 tended by the increasing size of the egg, and pressed against the 

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

 month, the decidua vera and decidua 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 a thin, friable, 

 semi-opaque layer, in which no glandular structure is perceptible. 



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

 Then, the time for parturition having arrived, the hypertrophied mus- 

 cular walls of the uterus contract upon its contents, expelling the foetus, 

 together with its membranes and the decidua. 



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

 are usually ruptured during parturition ; and the fetus escapes first, the 

 placenta and appendages following a few moments afterward. Occa- 

 sionally the egg is discharged entire, the foetus being afterward liberated 

 by the laceration of the membranes. In each case the mode of expulsion 

 is essentially the same. 



The process of parturition 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 blood-vessels, and separates without perceptible hemor- 

 rhage. The portion forming the placenta is, on the contrary, exces- 

 sively vascular ; and when this organ is separated, and its maternal 

 vessels torn off at their insertion, a gush of blood takes place, accom- 

 panying or immediately following the birth of the foetus. This normal 

 hemorrhage, at the time of parturition, does not come directly from 

 the uterine vessels. It consists of the blood contained in the placental 

 sinuses, and expelled from the placenta under the pressure of the 

 uterus. Since the blood thus lost was previously employed in the 

 placental circulation, and since the placenta is itself thrown off at the 

 same time, no unpleasant effect is produced by such a hemorrhage, 

 because the quantity of blood in the rest of the vascular system re- 

 mains the same. In normal parturition the lacerated uterine blood- 

 vessels are immediately closed, after separation of the placenta, by the 

 contraction of the muscular fibres through which they pass in an 

 oblique direction. Hemorrhage in delivery becomes injurious only 

 when it goes on after separation of the placenta ; in which case it is 

 supplied by the mouths of the uterine blood-vessels, left open by 

 failure of the uterine contractions. So long as the uterus remains 



