248 CLINICAL APPLIED ANATOMY. 



space by the seventh year. Until the fourth year it lies outside 

 the line of the nipple, but should not pass more than three- 

 quarters of an inch beyond this. From the fourth to the ninth year 

 it beats in the nipple line. After the thirteenth year the impulse 

 may be expected to occupy the same position as in the adult. 



In the erect posture in the adult, the impulse should appear 

 in the fifth left intercostal space, close above the sixth rib. It is 

 three and a half inches from the mid-line in the male and three 

 inches from the same line in the female. The area of impulse 

 should not be quite so large as that of a circle an inch in 

 diameter ; in other words, it is completely covered by the bell 

 of an ordinary stethoscope. The impulse may be made more 

 apparent by leaning forwards. It may appear in the fifth inter- 

 space in recumbency, and yet in the erect position be found 

 displaced behind the sixth rib, a fact which should lead to 

 examination of patients in both postures if possible. Even 

 though the heart is enlarged the actual apex may be so concealed 

 by the left lung as not to be felt until the patient is turned well 

 over on to the left side ; this often causes the impulse to appear 

 far back in the axilla in such cases, and gives some idea of the 

 increase in size of the heart. 



In old age the impulse is often displaced downwards into the 

 sixth intercostal space, the heart being depressed by elongation of 

 the ascending aorta in consequence of senile changes. (Fig. 25.) 



The position of the normal impulse is often loosely defined as 

 being in the fifth intercostal space a little below and internal to 

 the nipple. The variable position of the nipple is a defect in 

 this method of localising the position. The nipple should lie on 

 or just below the fourth rib, four inches from the mid line of the 

 body. When the breasts are enlarged or pendulous, the relations 

 of the nipple are subject to considerable alteration. 



The cardiac impulse is normally caused by the left ventricle, 

 and, being superficial, affords important indications as to the 

 condition of the wall of that cavity, becoming heaving in hyper- 

 trophy and feeble and diffuse in dilatation. In diseased con- 

 ditions other parts of the heart may give rise to* appreciable 



