THE CIRCULATION 



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valved. Then the auricles quickly shrink in all dimensions, and 

 as soon as their contraction is at its height the ventricles 

 contract, while the auricles relax. The ventricular wave runs 

 from base to apex too rapidly to be followed with the eye, 

 and ends, owing to the involution of the fascicles, in the musculi 

 papillares. As soon as ventricular systole has commenced, the 

 auricles relax. After emptying their contents into the aorta 

 and pulmonary artery, the ventricles relax, their contraction 

 giving way first at the apex, and being longest held at the base. 

 Then follows a pause (diastole), during which both auricles and 

 ventricles are flaccid. If the pericardium is open, the heart is 



Fm. 11. A SECTION APPROXIMATELY AT BIGHT ANGLES TO THE LONG Axis OF THE HEART, 



EXPOSING THE FOUR VALVES WHICH LIE VERY NEARLY IN THE SAME PLANE. 



The semilunar valve which guards the aperture of the pulmonary artery is the nearest to the 



breast-bone. 



seen to become round instead of oval in transverse outline 

 during systole. It shortens. Its apex twists a little to the right, 

 and projects forward. But if it is within its pericardium the 

 shortening is not accompanied with any displacement of the 

 apex. Instead of the apex mounting, the base descends. The 

 front of the right ventricle, at some little distance from the 

 apex, presses the chest-wall forwards in the fifth intercostal 

 space, about an inch to the inner side of a line falling vertically 

 through the nipple. This pressing forwards is felt as the 

 " impulse of the heart." 



The contraction of the heart is not a see-saw of auricles and 

 ventricles. During diastole blood is falling from the veins 



15 



