THE HEART 297 



apparent increase in the vertical extent may be due to the 

 persistence of a large thymus. 



Decrease in the size of the area of superficial cardiac 

 dulness can only be due to one cause, namely, emphysema. 

 This condition affects the least supported parts of the lungs, and, 

 therefore, the thin anterior borders are always involved at an 

 early stage. The margins of the incisura cardiaca are especi- 

 ally liable to be involved, as they can be greatly distended 

 without necessitating stretching of the parietal pleura 

 (Fig. 1 06). 



With the exception of the area of superficial cardiac dulness, 

 the whole of the antero-superior surface of the heart is covered 

 by the margins of the lungs, which, in this situation, are not 

 thick enough to obscure the dull cardiac note on firm per- 

 cussion over the cardiac area. On this account, the position 

 of the right and left borders of the heart can be determined 

 by percussion, but it is practically impossible to determine 

 the position of the lower border by percussion alone, as the 

 dull cardiac note merges into the dull note of the livtr. 



In dilatation or hypertrophy of the right ventricle the lower 

 border of the heart is displaced in a downward direction. 

 Although this alteration may not be easy to detect by means 

 of percussion, inspection alone may be of great value in 

 determining the condition. The downward enlargement 

 produces well-marked pulsation in the epigastrium, and the 

 character of the pulsation is quite different from that due to the 

 abdominal aorta in neurasthenic patients or to aneurism of 

 that vessel. In enlargement of the right ventricle, the 

 collapse or recession of the epigastrium synchronises with 

 ventricular systole, as it is due to the diminution of the 

 chamber in volume during the contraction. On the other 

 hand, in epigastric pulsation due to the abdominal aorta the 

 forward movement of the epigastrium synchronises with 

 ventricular systole. 



As the right ventricle enlarges, the left ventricle is displaced 

 in a backward direction and the apex-beat can no longer be 



