THE HEART 



35 



the valves curl in and lie so close to their fellows that nothing 

 can escape upwards into the auricles (Fig. 16). This may be 

 readily demonstrated in the dead heart by tying the aorta and 

 pulmonary veins, and introducing into the left auricle a tube 

 which admits a powerful jet of water ; the left side of the heart 

 distends and hardens, and at last water forces its way out of 

 the hole in the auricle through which the tube is inserted. If 

 the auricle be now opened, the ventricle is found cut off from 

 view by a tense membranous parachute-like dome, convex 

 towards the auricle, which is the mitral valve in position ; not a 



r aur.-~ 



vent 



Fig. 15. — Diagram to illustrate the Action of the Valves of the Heart 



(Huxley). 



In A the auricle is contracting, ventricle dilated, mitral valve open, semilunar 

 valves closed. In B the auricle is dilated, ventricle contracting, mitral valve 

 closed, semilunar valves open. Aur., auricle ; vent., ventricle; v., v., vein ; 

 a., aorta ; m., mitral valve ; s., semilunar valve. Note the manner in which 

 the papillae have shortened in B, in order to compensate for the approxima- 

 tion of the ventricular walls to the surfaces of the mitral valve. 



drop of water will escape from the ventricle, though the heart be 

 turned upside down, and it requires some little force to depress 

 the valve. 



During the filling of the ventricle the auriculo - ventricular 

 valves are coming into position; the blood is under them, and 

 the final systole of the auricle, by raising the pressure in the 

 ventricles, forces these valves into their place, and bulges them 

 upwards towards the auricular cavity. We have seen that even 

 in the dead heart their fit is so perfect that they render the 

 ventricle water-tight. But in the living heart the walls of the 

 ventricles are approximating as they contract on their contents. 



