252 CLINICAL APPLIED ANATOMY. 



to the level at which the ascending aorta, in consequence of its 

 forward inclination, comes nearest to the back of the sternum. 

 An aortic systolic murmur is often loudest in this situation, but 

 a faint diastolic murmur may be easily overlooked if only sought 

 for at this spot. Diastolic aortic murmurs are conducted down- 

 wards over the left ventricle towards the impulse of the heart ; 

 systolic murmurs are conducted along the ascending aorta to the 

 great arteries at the root of the neck. The forcible distension 

 of the sinuses of Valsalva with blood during the elastic recoil of 

 the aorta and other arteries in diastole occasionally drives air 

 out of the overlying lung with a slight puff and simulates a 

 diastolic murmur. Systolic murmurs may be produced in a 

 similar manner. These exocardial murmurs may generally be 

 recognised on account of the marked way in which they vary 

 with the respiration. 



The aortic valve segments are supported by a complete and 

 strong fibrous ring, which offers great resistance to dilatation of 

 the orifice. It is far more common for the mitral valve, which 

 lies next behind the aortic in the circulatory circuit to give way 

 under the stress of high back pressure. When dilatation does 

 occur at the aortic orifice it is usually the result of degenerative 

 lesions in later life. Paradoxically a dilated aortic orifice may 

 give rise to a systolic murmur, indicating obstruction, as well as 

 to the diastolic murmur of regurgitation. The obstructive 

 murmur may be due to the tight stretching of the valve cusps 

 across the lumen of the enlarged vessel. 



The base of the anterior segment of the mitral valve is struc- 

 turally continuous with the bases of the aortic cusps, so inflamma- 

 tion can and does often extend by continuity from the one valve 

 to the other. The orifices of the coronary arteries lie behind the 

 aortic valve segments, and although this position may shelter 

 them from emboli, it renders them liable to implication in aortic 

 disease, and adds to the gravity of the situation. 



When the aortic orifice is obstructed or the valve incompetent, 

 changes take place in the surface relations of the left ventricle. 

 In stenosis, these may be the result of pure hypertrophy, but in 



