THE HEART 299 



in the adult, the apex-beat is found in the fifth intercostal 

 space medial to the nipple line, in children under the age of 

 four it is usually situated in the fourth intercostal space 

 and it lies lateral to the nipple line. 



Surface Relations of the Valves of the Heart The 

 pulmonary valve lies behind the upper border of the third 

 costal cartilage of the left side, close to its articulation with 

 the sternum, and the aortic valve lies on a level with the lower 

 border of the same cartilage, but the latter lies nearer to the 

 median plane. Thus the orifice of the pulmonary artery, 

 which arises from the right ventricle, is situated to the left 

 side of the orifice of the aorta, which arises from the left 

 ventricle. This apparent contradiction is accounted for by 

 the obliquity of the interventricular septum, which slopes 

 backwards and to the right. 



The left atrio-ventricular (mitral) orifice is placed behind 

 the left half of the sternum, opposite the sternal ends of the 

 third interspace and the fourth costal cartilage, and it is dis- 

 posed obliquely so that the blood is directed forwards, down- 

 wards and to the left as it passes from the atrium into the 

 ventricle. The right atrio-ventricular (tricuspid) orifice lies 

 behind the right half of the sternum opposite the fourth cartilage, 

 the fourth interspace and the fifth cartilage. 



The accurate topography of the valves themselves is not of 

 very great importance in auscultation, as they are placed so 

 close to one another that, on auscultation directly over them, 

 it may be impossible to decide at which orifice a particular 

 sound is produced. On this account, the sounds produced 

 by the closing of the valves are ausculted over areas which 

 are widely separated from one another, and which are placed 

 over the chamber or vessel connected with the valve in 

 question. 



The pulmonary area lies behind the sternal end of the left 

 second interspace, and in this situation the pulmonary artery 

 is separated from the surface only by the thin anterior border 

 of the left lung. The aortic area lies over the right second 



