182 THE CIRCULATORY APPARATUS 



the auricles and ventricles empty their cavities of 

 blood into the pulmonary and arterial systems from 

 the right and left sides of the heart respectively. 

 Following this contraction wave is a pause or relaxa- 

 tion of the muscle the diastole during which time 

 the blood rapidly flows into the auricles and ven- 

 tricles, and at the end of the relaxation or diastole 

 there is a period of rest, during which time the auricles 

 and ventricles, or, in fact, the whole heart, is quietly 

 filling with more blood, when the phenomenon is 

 resumed. 



The Part Played by the Heart Muscle and Valves 

 during the Course of the Blood through the Chambers 

 of the Heart. We will start by allowing that the 

 contraction or systole of the ventricle has occurred. 

 Instantly the column of blood forced into the aorta 

 and pulmonary artery, by filling the sinuses of Val- 

 salva, forces the margins of the semilunar valves 

 together and prevents the return of the blood to the 

 ventricles from the aorta and pulmonary artery; 

 while the ventricle contraction or systole was emptying 

 its chambers, the auricles were filling from the vense 

 cavse and pulmonary veins, and this blood was rapidly 

 passed into the ventricles during the relaxation or 

 diastole, while a new supply has taken its place in 

 the auricles, the ventricles becoming distended with 

 more blood (during the period of rest) force upward 

 the tricuspid and mitral valves, gradually closing the 

 auriculoventricular openings. Suddenly the auricles 

 contract or begin their systole, and more blood is 

 forced into the ventricles, the valves close; immedi- 

 ately the ventricular systole or contraction takes 

 place, the, blood not being able to pass back into the 

 auricles owing to the closure of the auriculoventricular 

 openings, is forced into the aorta and pulmonary 

 artery, when the semilunar valves are flattened against 

 the walls by the pressure from the blood in the ven- 

 tricles. Now the ventricular systole is completed, the 



