266 



MANUAL OF PHYSIOLOGY. 



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

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

 pockets with free semilunar margins looking toward the vessel. 

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

 of the ventricle, with the lining membrane of which it is con- 

 tinuous. 



FIG. 117. 



m.v.a 



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 thieads attached to 

 the chord* tendineae. (Huxley.) RAV. Right auriculo-ventricular opening sur- 

 rounded by the flaps of tricuspid. LA V. Left auriculo-ventricular opening and attached 

 mitral valve. PA. Pulmonary valves when closed. AO. Aortic valves closed. 



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 

 blood stream for the air current ; the tendinous cords acting as 

 the "sheet" or rope which restrains the sail when filled with 

 wind. 



When the blood begins to pass in from the auricle, the valves 

 may be considered as lying against the ventricular wall. As the 



