HEART AND BLOOD-VESSELS. 



11 



th3 bulb, the ventricle ; the tube of exit, the artery ; and the pressure on 

 the bulb is effected by the contraction of the muscular walls of the heart, 

 at more or less regular intervals of, in the horse, about 40 in the minute. 



Starting at the left ventricle, we find that the blood contained in it, being 

 prevented by the valve of that side from entering the left auricle, is driven 

 by the contraction of the heart through the arteries, capillaries, and veins 



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Diagram of the circulation of blood. 



of general circulation, into the right auricle, from which it escapes past the 

 valve of the right side, into the right ventricle. It is then driven by the 

 contraction of the right side of the neart, which occurs simultaneously with 

 that of the left side, through the arteries, capillaries and veins of the pul- 

 monary circulation, until it flows into the left auricle, and finally past the 

 left valve into the left ventricle, where it completes its circuit, to be again 

 pumped round in the same way. The blood of the horse takes about 31 

 seconds of time, and about 27 contractions of the heart to complete the 

 entire round. 



