296 THE VASCULAR SYSTEM 



the second left intercostal space, about half an inch from the 

 left margin of the sternum. This line corresponds to the 

 margin of the left ventricle, but at its upper end it outlines 

 the left auricle (auricular appendix). 



The area which is mapped out by these borders corre- 

 sponds to the antero-superior surface of the heart. The 

 greater part of this surface is covered by the anterior margins 

 of the lungs, but, owing to the presence of the incisura 

 cardiaca (p. 349) on the left side, a small part is not covered 

 by the left lung. This small area consequently yields a dull 

 note on light percussion, and is termed the area of superficial 

 cardiac dulness. It is roughly triangular in shape. Its right 

 border is situated in the median plane and extends from the 

 level of the fourth to the level of the sixth costal cartilage, a 

 distance of about i-J inches. From this line the area of 

 superficial dulness can be traced to the left, but it rapidly 

 diminishes in vertical extent. The lower border of the area 

 coincides with the intermediate portion of the lower border of 

 the heart, and the upper border descends to meet it at a point 

 about i inch medial to the apex-beat (Fig. 106). In map- 

 ping out the area of superficial cardiac duiness very light 

 percussion is employed, because of the thinness of the adjoin- 

 ing lung margins. 



Although no part of the area of superficial cardiac dul- 

 ness is covered by lung, that part of it which lies beyond 

 the left side of the sternum is covered by the left pleural 

 sac. 



Increase in the size of the area of superficial cardiac dulness 

 may be due to one of several causes. Factors which tend to 

 cause the lungs to retract or collapse, e.g. pulmonary tubercu- 

 losis, pneumothorax, pericardial effusions, cardiac hypertrophy, 

 etc., produce a real increase in extent. Left- or right-sided 

 pleural effusions, when they rise as high as the sternal 

 extremity of the fifth costal cartilage, increase the lateral 

 extent of the area, but the increase is not a true increase inas- 

 much as it is not formed by the heart. In young children, an 



