MITEAL INCOMPETENCE. 253 



incompetence, the ventricle is usually as much dilated as hyper- 

 trophied. In both cases the outer boundary of the ventricle is 

 carried to the left, and the cardiac impulse displaced downwards 

 and outwards. The outward displacement of the left margin of 

 the ventricle will increase the area of superficial cardiac dulness 

 towards the left owing to the retraction of the lung from the 

 surface of the enlarging heart. When the left ventricle is much 

 hypertrophied and the right chambers of the heart are as yet 

 but slightly involved, the impulse of the left ventricle can some- 

 times be felt in the epigastrium, but this is exceptional ; an 

 epigastric impulse as a rule is caused by the right ventricle. 



Mitral Incompetence. The mitral valve lies behind the 

 sternum, opposite the attachments of the fourth costal cartilages. 

 The right ventricle intervenes between it and the back of the 

 bone. The systolic murmur of mitral incompetence is best 

 heard at the cardiac impulse, this being the spot where the left 

 ventricle comes nearest to the surface of the chest. The murmur 

 may be traced towards the axilla, gradually fading away as the 

 ventricle recedes, and a thicker wedge of lung becomes interposed 

 between the heart and the parieties of the thorax. The murmur 

 may in some instances be heard at the back between the scapula 

 and the spine ; it is probably conducted to this spot by an 

 independent route, for that part of the base of the left ventricle 

 which lies immediately below the left auricle rests directly on the 

 structures in front of the spinal column. The murmur is 

 therefore said to be conducted by the vertebrae from the base or 

 " shoulder " of the left ventricle. Another explanation attributes 

 the conduction of the murmur to the back to the presence here 

 of the left auricle which receives the regurgitant stream of blood. 



A systolic murmur may exist at the mitral orifice even though 

 the valve cusps are not diseased. The ring of fibrous tissue 

 which supports the valve segments takes its origin from the 

 central fibro-cartilage of the heart. On the side of the orifice 

 which lies remote from the fibro-cartilage, the fibrous ring is 

 exceedingly thin and cannot offer much resistance to stretching. 

 Consequently the mitral valve depends for its competency on the 



