256 CLINICAL APPLIED ANATOMY. 



the left, which thus prevents the normal conduction of the aortic 

 second sound to the apex by the left ventricle. It is said that 

 the pulmonary second sound is always inaudible at the impulse. 

 Moreover, in mitral stenosis the aorta is insufficiently filled, 

 its elastic recoil is consequently less and its second sound is 

 fainter. 



The left auricle, lying as it does immediately behind the site 

 of obstruction, may attain a great size and is usually enlarged 

 in all its diameters. Being interposed between the ventricle and 

 the spinal column, it may actually, when distended, indirectly 

 play a part in production of the cardiac impulse, by thrusting 

 the ventricles forwards. In such exceptional cases the com- 

 mencement of the impulse is really presystolic in time. 



Upward enlargement of the left auricle may raise the roots of 

 the lungs and actually exercise some pressure on the bronchi, 

 since the latter are in contact with the upper part of the posterior 

 surface of the auricular chamber. Lateral enlargement of the 

 left auricle has been supposed to give rise to an outward extension 

 of cardiac dulness in the third and fourth left interspaces, but 

 this dull area is more correctly assigned to an upward enlarge- 

 ment of the conus arteriosus of the right ventricle. In some 

 instances of great enlargement transversely, the left auricle has 

 been found pulsating to the right of the sternal edge, having 

 passed across the back of the right auricle, to which it is normally 

 posterior, and then gained the surface on the right side. This 

 great transverse or horizontal enlargement is usually rather 

 associated with carditis and pericarditis than with mitral stenosis. 



The pulmonary veins, which return the oxygenated blood from 

 the lungs to the left auricle, dilate on account of the increased 

 pressure in the latter cavity and may show patches of athero- 

 matous change. 



The obstruction to the pulmonary circulation causes the right 

 ventricle to hypertrophy and dilate in its turn, and the muscular 

 mass of this cavity is a very important factor in maintaining the 

 circulation through the constricted mitral orifice. The right 

 ventricle forms the greatest part of the anterior surface of the 



