568 THE PHYSIOLOGY OF REPRODUCTION 



amount of haemorrhage, which is represented in normal cases by from 

 three to four hundred cubic centimetres of blood. 



The duration of labour shows considerable variation, but is 

 generally longer in primiparous women (i.e. those who have never 

 borne children before) than in multiparous ones. The average for 

 the former is rather more than eighteen hours, the three stages 

 respectively occupying sixteen, two, and from a quarter to half-an- 

 hour. The average for multiparous women is twelve hours, eleven 

 of which are occupied -by the first, and one by the second stage. 

 The duration of labour in primiparous women depends also upon 

 age, being usually more prolonged in elderly subjects. 



PARTURITION IN OTHER MAMMALIA 



In animals the process of delivery varies somewhat in the different 

 animals. In the horse the foetus, which has been lying on its back 



FIG. 158. The first stage in the revolution of the equine fcetus. The os is 

 dilated by the membranes, which have not yet ruptured. (After Franck. 

 From Smith's Veterinary Physiology, Bailliere, Tindall & Cox.) 



during intra-uterine life, preparatory to birth changes on to its side 

 and afterwards assumes the upright position, with its muzzle and 

 forelegs in the direction of the pelvis. Dilatation of the passage 

 follows, and the foal is delivered head first. In the cow and sheep 

 the movements which occur are essentially similar. It is stated that 

 the alteration in the position of the foetus is not brought about by 

 its own movements but by the uterine contractions. The revolution 

 of the foetus prior to birth in the mare and cow is apparently 

 responsible for the torsion of the neck of the uterus which often 

 occurs in these animals. 



Parturition in the mare is accompanied by a complete separation 

 of the chorion from the uterine wall. As a consequence of this fact 



