THE ANIMAL MACHINE 21 



blood of the dam are passed by osmosis into the foetal cir- 

 culation, 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 fcetus is nourished until after 

 birth, when the establishment 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 



D 



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 

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

 perineal regions, followed by labor. Normally the fcetus is 

 presented head first, with the chin resting on the extended 



