THE PHENOMENA NOTED DURING EACH CARDIAC CYCLE 283 



Fig. 140. — Transverse Section 



Through the Chest to Show the 



Changes in the Shape of the Base 



OF THE Heart on Systole. 



The systolic heart (dotted line) lies 



closer to the chest wall. 



fourth intercostal space and is not so clearly betrayed on account of 



the interposition of a layer of mammary tissue. The area so affected 



measures about 2 cm. in diameter. 

 In accordance with the statements 



just made, it is possible to assign 



three causes to this impulse, namely: 



(a) the change in the outline of the 



basal portion of the heart, (h) the 



elevation or erection of the ventricle, 



and (c) the spiral rotation of the apex 



from left to right and from behind 



forward. We have seen that the 



cross-section of the base of the dias- 

 tolic heart is elliptical while that of 



the systolic organ is circular. This 



change, as is clearly portrayed in the 



accompanying schema (Fig. 140), 



tends to decrease the distance between 



the wall of the thorax and the anterior surface of the heart. The base 

 of the organ is thus moved nearer the chest wall. It 

 should also be remembered that, in man, the space 

 intervening between the heart and the wall of the 

 thorax, is filled by the marginal area of the left lung. 

 As this organ is more fully distended during inspira- 

 tion, its border is forced farther forward in the direc- 

 tion of the median line, while during the subsequent 

 expiration it again recedes laterally. It may be in- 

 ferred, therefore, that the layer of pulmonary tissue in- 

 terposed between the heart and the thoracic wall, is 

 thinner during expiration than during inspiration and 

 that the organ as a whole approaches the thoracic 

 wall more closely during the former period. For this 

 reason, the cardiac impulse, or apex beat, is more con- 

 spicuous during expiration. In the second place, it 

 need scarcely be emphasized that the ventricle is more 

 flaccid when relaxed than when contracted, so that its 

 apex must assume a more dependent position during 

 the former period. The contraction of the ventricle, 

 therefore, must lead to an elevation of the apex for- 

 ward and upward,^ because the base of the organ is 

 naturally more firmly anchored than its apex (Fig. 141). 

 Thirdly, this upward kick of the ventricle is intensi- 

 fied by the fact that the apex turns slightly around 

 its longitudinal axis, bringing a more extensive por- 

 tion of its left side into view.^ 



Fig. 141.— 

 Longitudinal 

 Section Through 

 THE Chest to 

 Show the For- 

 ward and Upward 

 Movement of the 

 Apex During the 

 Systole (Dotted 

 Line) of the Ven- 

 tricles. 



^ W. Harvey, 

 ^ W. Harvey, 



'Cor sese erigere." 

 ■lateralem inclinationem. 



