THE ANIMAL MACHINE 



21 



is passed into the foetal circulation, through the arteries 

 of the umbilical or navel cord and back through the veins 

 of the same structure into the general venous circulation 

 of the dam, to begin another cycle. By this means the 

 foetus is nourished until after birth, when the establish- 

 ment of respiration and digestion enables him to aerate 

 his own blood and nourish his own tissues. All connection 

 with his mother is cut off with the severing of the cord, 

 which takes place soon after birth. 



26. Parturition. — Parturition is accomplished by the 

 general relaxation of the ligaments which unite the bones 



Fig. 10. — Pelvis of the mare, showing the dimensions of the pelvic 

 girdle through which the foetus passes in delivery. A , coupling ; 

 B, point of the hip ; C, hip joint ; D, point of the buttocks. 



constituting the pelvic girdle (Fig. 10), through which the 

 foetus must pass, and the soft structures of the pelvic and 

 perineal regions, followed by labor. Normally the foetus is 

 presented head first, with the chin resting on the extended 



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