A STUDY OF THE CIRCULATION OF BLOOD 133 



valve flaps, and at the other to muscular elevations (the 

 pap'iUa-ry muscles) on the inner walls of the ventricle. The 

 length of the cords is regulated by these muscular papillae in 

 such a way that in a healthy heart the valves, when closed, 

 do not allow a drop of blood to return to the auricle. In 

 certain kinds of heart disease these flaps do not act prop- 

 erly, and then the skilled ear of the physician, listening at 

 the wall of the chest, can detect at each heart beat the 

 " murmur " caused by the backward rush of the blood. 



The valve in the left heart works on the same principle 

 as the tricuspid valve we have just described. It consists, 

 however, of but two flaps. From its fancied resemblance to 

 a bishop's mitre it has received the name ml'tral valve. 



The Blood Vessels connected with the Right Heart. The 

 function of the right heart, as we have already suggested, is 

 that of pumping the blood, received from the various organs 

 of the body, to the lungs. Connected with the right auricle 

 'are two large blood vessels ; one brings in the blood from the 

 organs in the lower part of the body (liver, stomach intes- 

 tines, kidneys, feet), and is called the in-fe'ri-or ve'na ca'va 

 (Latin inferior = lower -f cava = hollow + vena = vein) ; the 

 other, the su-pe'ri-or ve'na ca'va, pours into the right auricle 

 the blood from the head, the arms, and the upper part of the 

 trunk. All this blood is a dark red or purplish color, because 

 it has given up its oxygen to the various tissues from which 

 it has come. It must therefore load up with oxygen be- 

 fore it can again supply this ever needed element. The new 

 supply of oxygen is secured in the lungs. 



From the right auricle the blood first goes into the right 

 ventricle ; then it is forced into a large blood vessel called 

 the pul'mo-na-ry artery (Latin pulmonarius, referring to the 

 lung). Soon after leaving the heart the pulmonary artery 

 divides, giving off a branch to each lung (see Figs. 4749). 



The Semilunar Valves. The pulmonary artery is always 

 full of blood, and when the ventricle contracts, this blood ves- 

 sel has to be stretched in order to accommodate the additional 



