VALVES OF THE HEART 



377 



mitral valve on the left side of the heart has only two triangular 

 flaps like a bishop's mitre, while, on the other hand, the passage 

 way from right atrium to right ventricle is guarded by the three 

 cusps of the tricuspid valve. 



During systole, the strong anterior cusp of the mitral valve 

 does not materially shift its position. The other cusp is pulled 

 forward against it. 



On the right side, one of the cusps hangs down on the septum 

 and is practically immovable. The other two cusps arc pulled 

 over towards the septal cusp. The mass of blood pressing on the 

 sides of the cusps completes the closing of the orifice. 



When this mass of blood, under the pressure induced by the 



CORPUS ARANTll 



Fig. 89. — Semilunar valves. A, in longitudinal-mesial section. B, Artery laid open and 

 exposed, and C, closed valves from the arterial aspect. 



contraction of the ventricles, stretches the atrio-ventricular valves 

 it causes them to emit a sound which is a component of the first 

 sound of the heart. The other component is the sound produced 

 at the same time by the contraction of the ventricular walls. 

 It is said that a trained ear can pick out the notes due to closure 

 of the valves from those due to stretching of the muscular walls. 



(2) Semilunar Valves. The valves situated at the openings of 

 the ventricles into the arteries are similar in shape and in action 

 to the pocket valves of the veins (Fig. 89). Each is composed of 

 three pockets or half cups attached along their curved margins to 

 the walls of the artery and upper part of the ventricle and with their 

 openings set away from the ventricle. 



The cusps are not placed all exactly on the same plane. One 

 cusp lies somewhat deeper in the heart than the others. This 



