INVOLUTION OF THE UTERUS 81 



III. 



INVOLUTION OF THE UTERUS. 



After the young has been born, its envelopes are still 

 united to the uterine mucous membrane. As soon as the 

 uterus contracts after parturition, circulation ceases in the 

 envelopes. 



All foetal membranes are termed after-birth, or placenta, 

 as their expulsion takes place soon after birth. The stage 

 during which they are expelled might be termed port-partum 

 period. Parturition therefore can be divided into the prelim- 

 inary, expulsive and post-partum stage. 



I. — EXPULSION OF THE FCETAL MEMBRANES. 



The fcetal envelopes are still connected with the uterus by 

 the fcetal placentae. The chorion attaches itself, as previously 

 explained, to the maternal placentas, or cotyledons. 



We know that on the surface of the cotyledons the villi of 

 the fcetal placenta dip between those of the maternal placenta. 

 The concave fcetal placentas surround the maternal placenta 

 like a pot. As long as the circulation exists, the villi of either 

 are filled and pressed against each other. The exchange of 

 nutritive elements occurs at the bright seam between the 

 placental villi, which is formed by the uterine milk, cessation 

 of circulation following uterine contractions after parturition 

 loosens the union between the villi. Already the circulatory 

 changes disturbed the union between the chorion and cotyle- 

 dons. 



The expulsion is effected by contractions of the uterus — 

 the so-called after-pains or dolores post-partum. The cotyle- 

 dons do not contain any muscular bundles. Therefore the 

 conditions for the detachment of a multiple placenta are less 

 favorable than for those of a disseminated one. The numerous 

 placentas of the cow do not separate from the uterus simul- 

 taneously, but one after the other. 



