ObO MANUAL OF PHYSIOLOGY. 



that when the placenta separates from the uterine walls, the 

 arterioles leading to the sinuses are contracted and possibly 

 occluded with clots. The uterine blood current is thus prevented 

 from escaping into the uterine cavity after parturition, and caus- 

 ing profuse hemorrhage. 



The uses of the placenta may be briefly summed up as : 



(1) Alimentary, as it supplies the place of the alimentary 

 canal. 



(2) Respiratory, as it performs the function of the lungs.' 



(3) Excretory, as it does duty for the kidneys and some other 

 excretory organs. 



