260 



MANUAL OF PHYSIOLOGY. 



hence it is called the "tricuspid" valve (Fig. 117, RAV). The 

 opening from the left auricle to the left ventricle, which is about 

 one-third smaller, is guarded by two large valvular flaps, and is 

 hence called the "bicuspid," or more commonly "mitral" valve 

 (Fig. 116). The arterial valves are made up of three deep pockets 

 with free semi-lunar margins looking towards the vessel. The 



m.v.t 



LAV 



RAV 



The Orifices of the Heart seen from below, the whole of the ventricles 

 being cut away, and the curtains of the auriculo-ventricular valves drawn 

 down by threads attached to the chorda tendinese. (Huxley.) RA V. Right 

 auriculo-ventricular opening surrounded by the flaps of tricuspid. LA V. 

 Left auriculo-ventricular opening and attached mitral valve. PA. Pul- 

 monary valves when closed. AO. Aortic valves closed. 



curved base of each pocket is attached to the arterial orifice of 

 the ventricle, with the lining membrane of which it is continuous. 



ACTION OF THE VALVES. 



The mode of action of the flaps of the tricuspid and mitral 

 valves is like that of a lateen sail of a boat, if we substitute the 



