PHYSIOLOGY. 43 
passage, or it may pass outside, without rupture, 
In any. case, it is shortly followed by the two fore- 
feet of the foetus, with the head resting between them 
at the fetlocks. When the point of the withers of the 
foetus appears at the entrance of the pelvic cavity, a 
few more slight contractions complete parturition. 
Sig 
= 
Fic. 19. 
NorMAL PosITIoN OF THE Fetus IN THE Mare (THIRD STAGE), 
VERTEBRO-SACRAL POSITION. 
Parturition is quite a normal function, when 
performed in the manner described. When the fcetus 
has been fully developed in the uterus, there is a 
gradual determination of its blood supply to the 
mamme of the parent. A number of the vascular 
connections are then no longer needed between the 
uterus and the placental memibranes, and fatty degene- 
ration of these takes place. This alteration is believed 
to have some special action on the nerve filaments in 
the uterine walls, which (filaments) become irritated, and 
through them the walls of the uterus are stimulated to 
