254 CLINICAL APPLIED ANATOMY. 



transverse contractile power of the cardiac muscle rather than on 

 the strength of its own fibrous foundation. Temporary weakness 

 of the cardiac muscle therefore may occasion temporary mitral 

 incompetence which will disappear when the myocardium recovers 

 its normal tone. In conditions of high arterial tension such as 

 obtain in chronic renal disease and in arteriosclerosis a murmur 

 develops at the mitral orifice as the result of increased back 

 pressure, although the stronger aortic valve, which is more directly 

 exposed to the pressure, remains competent. 



Mitral incompetence early gives rise to dilatation and hyper- 

 trophy of the left ventricle and the left auricle. Since the left 

 auricle is interposed between the base of the left ventricle and the 

 structures immediately in front of the spinal column, it is not 

 accessible to clinical examination, but the rise of pressure in the 

 cavity, transmitted backwards through the pulmonary veins, 

 gives rise to an accentuation of the second sound at the pulmonary 

 orifice. The pulmonary valves are superficial and lie at the 

 upper border of the third left costal cartilage, at its junction with 

 the sternum. The "pulmonary cartilage" is the second left 

 costal cartilage, and marks the spot where the pulmonary artery 

 approaches nearest to the surface of the body before dividing 

 into its two large branches. The accentuated sound may be 

 heard either over the valves or over the pulmonary cartilage ; in 

 the former position the valve closure may also be felt. Hyper- 

 trophy and dilatation of the right ventricle and auricle follow in 

 turn. The results of increase in size of the left ventricle have 

 already been discussed in the section on aortic disease, but it 

 must be pointed out that the alteration of the position of the 

 cardiac impulse in mitral incompetence is the resultant of two 

 forces. The hypertrophy of the left ventricle displaces the 

 impulse downwards and somewhat outwards, whilst the hyper- 

 trophy of the right ventricle tends to displace it outwards, and 

 using the diaphragm as a fulcrum, even to lift it up. 



Mitral Stenosis. In mitral stenosis all the cavities of the heart, 

 with possibly the exception of the left ventricle, ultimately 

 become enlarged, and, if the occurrence of a pulmonary diastolic 



