90 ELEMENTS OF PHYSIOLOGY 



both sides of the heart at once, both auricles contracting 

 at the same time and then relaxing as the contraction 

 passes to the ventricles. 



148. As we learned, the pressure from the right ventricle 

 keeps the blood moving through the pulmonary artery, the 

 capillaries of the lungs, and the pulmonary vein ; it returns 

 to the heart again, and this time it enters the left auricle. 



149. When the left auricle is full, it contracts and drives 



m.v.a 



MAY 



FIG. 88. View of the Orifices and Valves of the Heart from below, the whole of 

 the two Ventricles being cut away. 



Ao, aorta; PA, pulmonary artery, each with its three cups of the closed semilunar valves 

 seen convex from below; RAV t opening between right auricle and right ventricle, 

 surrounded by the three flaps, t.v.i, t.v.-z, t ^.3, of the tricuspid valve with chordae tendineae 

 between them, to which three cords are tied, taking the place of the papillary muscles; 

 LA V, opening between left auricle and left ventricle, with the two flaps, m.-v. i, m.v. z 

 of the mitral valves and chordae tendinae, to which cords are tied. 



This figure may be said to show the roof of the two ventricles, with the two great valves 

 by which the blood enters the ventricles and the two great valves by which it leaves them. 

 All the openings of the ventricles are upward. 



the blood through a valve called the bicuspid (Fig. 88), 

 or mitral, valve, into the left ventricle. [Mnemonic : the 

 t(r)i cuspid is on the (r)ight side, the bicuspid on the left.] 

 The left ventricle (at the same time with its mate, the right 

 ventricle) then contracts, forcing the blood behind the flaps 



