EXPULSION OF THE FETAL MEMBRANES AND INVO- 

 LUTION OF THE UTERUS. 



The expulsion of the fetal membranes normally follows birth 

 after a very brief interval, depending upon the species of animal 

 and the individual. The expulsion of the fetal membranes occurs 

 most promptly in those animals like the mare, in which, owing 

 to the diffuse placenta, the attachments of the chorion to the 

 uterus are not so complex and consequently not so difficult 

 of detachment. In ruminants, with the mtltiple placenta or 

 cotyledons, the attachments between the fetal and maternal pla- 

 centa are very intricate and the placental villi very long and 

 branched, so that they do not so readily be.come detached from 

 the maternal organ. 



The detachment of the placenta is largely the result of the con- 

 traction of the uterine walls, which, acting upon the villi of the 

 fetal placenta, tends to force them out and detach them, while 

 the decrease in the size of the uterine cavity forces the detached 

 membranes out through the vagina. The contraction of the 

 uterine walls of ruminants cannot act so effectively upon the 

 cotyledons as can the walls of the uterus of the mare upon the 

 diffused tufts. The contraction or involution of the uterus and 

 the expulsion of the membranes are therefore correlated phenom- 

 ena which go hand in hand, and when one fails it tends to 

 interrupt the other. 



In the mare we have seen the entire placenta and all the fetal 

 membranes promptly expelled from the uterus, while the fetus 

 remained naked in the organ, because of some slight deviation of 

 a fetal part which prevented its ready expulsion. In this case 

 the contraction of the uterus, with the escape of the amniotic 

 and allantoic fluids, was sufficient to cause the detachment and 

 expulsion of the chorion. Fleming suggests that the same acci- 

 dent may occur in the cow, but this we have not okserved. Owing 

 to the character of the placenta in that animal, such an occurrence 

 must be extremely rare, except in cases of prolonged dystokia, 

 with decomposition of the membranes. 



In some cases of birth, in the mare, especially where there has 

 been a slight delay, the fetal membranes accompany the fetus or 

 follow it immediately. In cases of dystokia in the mare, as a 

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