126 ELEMENTARY PHYSIOLOGY 



a nipple). To these papilla are attached very fine tendinous threads (chordae 

 tendineae), which are again connected at their other and upper ends with thin 

 membranous flaps or cusps. The cusps are three in number, and lie loosely 

 against the walls of the ventricle, but it will be readily understood that a 



3" 



Fig. 1 1 8. -The Human Heart. The Left Auricle and Ventricle opened, 

 and part of the Wall removed to show the Interior. 



ventricle preserver! with a papillary muscle attached to it ; 5, papillary muscles ; 6 and 6 , 

 the segments of the mitral valve ; 7, the interior of the aorta, just above its semilunar 

 valves ; 7', the arch of the _aorta ; 8, the root of the pulmonary artery with its semilunar 

 valves ; 8', a separated portion of the pulmonary artery, remaining attached to the aorta 

 by a cord, 9 ; 10, branches of the aorta. 



pressure of blood in the ventricle would act on the under surfaces of these 

 cusps and cause them to rise. Under these circumstances the tendinous cords 

 are stretched, and the edges of the cusps meet so as to stop the communica- 



