282 



THE MECHANICS OF THE HEART 



tions in its shape, and secondly, to the alterations in its position. 

 Concerning the former, the general statement may be made that its 

 longitudinal and transverse diameters are decreased during systole, 

 while its anteroposterior diameter is increased. In this way, the base 

 and apex of the organ are brought closer together, while the outhne 

 of its basal portion is changed from an ellipse to a circle. For this 

 reason, a diastolic heart always appears to be thicker along its borders' 

 than near its center, while the organ as a whole more nearly conforms 

 to the general outline of the surface upon which it is resting. It is 

 also evident that the systolic heart executes a rotatory movement 

 which under ordinary conditions of experimentation remains more 

 closely confined to its apical portion. In accordance with our previous 



Fig. 139. — Showing Location of Apex Beat. 

 The position of the aortic semilunar ( +) and mitral (A) valves are indicated in red 

 and that of the pulmonary semilunar ( +) and tricuspid (A) in blue. 



observation that the superficial fibers of the ventricle pursue in general 

 an S-shaped course and form a whorl at the apex, it may be inferred 

 that the rotation takes place from left to right. 



The Cardiac Impulse (Impulsus Cordis). — On observing the exter- 

 nal surface of the chest in the region of the apex of the heart, it is 

 noticed that the thoracic wall is made to bulge outward with every 

 systohc movement. In men, the greatest prominence is attained in 

 the fifth intercostal space slightly to the right of the left mammillary 

 line, which represents the perpendicular drawn through the left 

 nipple. In woman, this impulse is more frequently observed in the 



