132 STUDIES IN PHYSIOLOGY 



great thickness of the former. The left ventricle does much 

 more work than the right ; it forces blood to the top of 

 the head, to the tips of the fingers and toes, and to every 

 other organ of the body. The right ventricle, on the other 

 hand, pumps blood only to the lungs. 



The Valves of thie Right and Left Hearts. We have described 

 the partition between the auricles and ventricles as mov- 

 able. In the right heart there are three triangular flaps of 

 connective tissue, attached to the sides of the opening from 



FIG. 48. Right Heart (opened) . FIG. 49. Left Heart (opened) . 



auricle to ventricle. This is the so-called tri-cus'pid valve 

 (Latin tri= three + cuspis = point). When the ventricle is 

 empty, these flaps tang downward ; but as the blood pours 

 in from the auricle, their free edges gradually float upward 

 until, when the ventricle is full, the three portions come 

 to lie horizontally. It is evident that when the ventricle 

 begins to contract, the blood would tend to push this valve 

 upward still further, thus allowing the blood to return 

 to the auricle. This is prevented, however, by a number of 

 strong cords of connective tissue (the chor'dce ten-din' e-ce), 

 that are attached at one end near the movable edge of the 



