188 



PHYSIOLOGY OF FARM ANIMALS 



[CH. 



lie on their backs within the uterus on the floor of the mother's 

 abdomen, but shorth' before birth the foetus turns on its side 

 taking a lateral position, and then turns still further assuming an 

 upright j)osition. The foetus is then brought into a position in 

 which the muzzle rests upon the fore legs, these being extended in 

 the direction of the vaginal opening, while the hind limbs are drawn 

 up under its body. This method of presentation (anterior or 

 'head presentation') is the most normal, but it often happens that 

 the hind legs appear first (posterior or ' breach presentation ') or the 

 foetus may be presented transversely or cross-wise. 



Fig. 98. Second position preparatory to parturition (after Franck from Fleming, 

 Messrs Bailliere, Tindall and Cox), a amnion, b allantois. 



The mother as the time for j)arturition draws near becomes 

 increasingly disturbed and restless, frequently changing her 

 position. When the actual 'pains' commence she shows evident 

 signs of distress, and the skin becomes hot and the pulse rate 

 rapid, but each 'pain' is succeeded by an interval of calm. 



The 'pains' are caused by the contraction of the longitudinal 

 muscles of the uterus which in this way dilate the os or mouth of 

 the uterus. Even in the virgin the uterine muscles undergo very 

 slight rhythmic contractions as may be seen when the organ is 

 withdrawn from the body and kept in salt solution at body tempera- 

 ture, and these contractions may be greatly increased by applying 



