392 A Manned of Veterina/ry Physiology. 



the largest of the two cornua, the fu j tus now assumes first a 

 lateral position, and lastly an upright one, Iry which the 

 fcetal and maternal spines are brought nearer together. To 

 assume this position, the foetus has had to make a complete 

 revolution ; it is now brought with the muzzle and fore-legs 

 in the direction of the pelvis, and the dilatation of the 

 os uteri follows. In the cow the foetus lies on its back on 

 the floor of the abdomen as in the mare, but lies somewhat 

 crooked, viz., the head inclining towards one side, and the 

 hind extremities towards the other ; in all other respects it 

 resembles the mare. The alteration in the position of the 

 foetus does not occur through its own movements, but by 

 the contraction of the uterus; on the other hand, the 

 stretching of the limbs is the result of foetal movement.* 



The dilatation of the os is assisted by the amniotic and 

 allantoic fluids ; each contraction of the uterus is accom- 

 panied by a pain ; the pains last from 15 to 90 seconds, 

 and the interval between them is from 2 to 4 minutes. 



The mare is remarkable for the rapidity with which 

 delivery is effected ; ruminants, on the other hand, are 

 often very slow, and in labour for hours. The rapid de- 

 livery of the mare is accompanied by a complete separation 

 of the chorion from the uterine walls ; this is the explana- 

 tion why any difficulty in foaling invariably sacrifices the 

 life of the foal. In ruminants, on the contrary, the circula- 

 tion between the mother and foetus is kept up to the last 

 by the gradual separation of the cotyledons, so that, though 

 calving may be delayed several hours, the calf may, and 

 commonly is, born alive. 



The contractions of the uterus occur through a centre 

 in the lumbar portion of the cord ; it is not under the 

 control of the will, and has the power of acting even 

 though the animal be unconscious. 



Mammary Secretion. 

 As the period of parturition approaches the mammary 

 glands become swollen, owing to the active changes occur- 



* The description of the change in the position of the foetus pre- 

 paratory to birth is takon from Bllenb xger's ' Physiologies 



