724 



A MANUAL OF VETERINARY PHYSIOLOGY 



fluids. Each contraction of the uterus is accompanied by a pain ; 

 the pains last from fifteen to ninety seconds, and the interval 

 between them is from two to four minutes. The contractions of the 

 uterus occur under the influence of a centre in the lumbar portion 

 of the cord ; they are not under the control of the will, and occur 

 even though the animal be unconscious, or the spinal cord divided 

 in the lower cervical region (dog). 



The mare is remarkable for the rapidity with which delivery is 

 effected ; ruminants, on the other hand, are often very slow and in 



Fig. 256. — The Revolution completed, Membranes ruptured, and Foal 

 in the Normal Position for Delivery (Franck). 



a, The Allantois ; b, the Amnion. 



labour for hours. Parturition in the mare is accompanied by a 

 complete separation of the chorion from the uterine wall ; this is 

 the explanation why any difficulty in delivery invariably sacrifices 

 the life of the foal. In ruminants, on the contrary, the circulation 

 between the mother and foetus is to the last kept up by the gradual 

 separation of the cotyledons, so that, though the process may be 

 delayed several hours, the animal is generally born alive. The 

 cause of the first respiration of the foetus is dealt with at p. 138. 

 Twin births are rare in the mare (in the thoroughbred approximately 

 eight per thousand), and few survive ; in the cow they are common. 



