ACTION OP THE VALVES. 



261 



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

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

 The blood driven in from the auricle at first pushes the cur- 

 tains of the valves against the ventricular wall, and immediately 

 fills the ventricle. As the ventricle becomes distended the tendi- 

 nous cords coming from the elastic papillary muscles are put on 

 the stretch, and draw the valve curtains away from the wall of 

 the ventricle into the midst of the fluid. When the ventricle 



FIG. 118. 



Ao 



iva 



The Orifices of the Heart seen from above, both the auricles and the 

 great vessels being removed. (Huxley.) PA. Pulmonary artery and its 

 semilunar valves. Ao. Aorta and its valves. RAV. Tricuspid, and LAV. 

 Biscuspid valves. 



begins to contract upon its contained blood, the pressure of the 

 fluid bellies out the sail-like valves towards the auricles, so that 

 their convex sides come into close apposition with one another. 

 Their free margins are held firmly by the papillary muscles con- 

 tracting and tightening the cords. The flaps are kept at much 

 the same tension by the papillary muscles shortening in proper- 



