CH. XX.] THE CORONARY ARTERIES 237 



arterial walls and the wire. Upon applying the stethoscope to the 

 vessels, after such an operation, the second sound ceased to be 

 audible. Disease of these valves, when sufficient to interfere with 

 their efficient action, also demonstrates the same fact by modifying 

 the second sound or destroying its distinctness. 



The contraction of the auricles is inaudible. 



The first sound is heard most distinctly at the apex beat in the 

 fifth interspace ; the second sound is best heard over the second right 

 costal cartilage that is, the place where the aorta lies nearest to 

 the surface. The pulmonary and aortic valves generally close simul- 

 taneously. In some cases, however, the aortic may close slightly 

 before the pulmonary valves, giving rise to a " reduplicated second 

 sound." The pulmonary contribution to this sound is best heard over 

 the second left cartilage. 



The Coronary Arteries. 



The coronary arteries are the first branches of the aorta; they 

 originate from the sinuses of Valsalva, and are destined for the supply 

 of the heart itself ; the entrance of the coronary vein, into the right 

 auricle, we have already seen (p. 207). 



Ligature of the coronary arteries causes almost immediate 

 death; the heart, deprived of its normal blood-supply, beats irregu- 

 larly, goes into fibrillary twitchings, and then ceases to contract 

 altogether. 



In fatty degeneration of the heart in man, sudden death is by 

 no means infrequent. This is in many cases due to a growth in 

 thickness of the walls of the coronary arteries called atheroma, which 

 progresses until the lumen of these arteries is obliterated, and the 

 man dies almost as if they had been ligatured. 



Self-steering Action of the Heart. This expression was originated by Briicke. 

 He supposed that the semilunar valves closed the orifices of the coronary arteries 

 during the systole of the heart. Unlike all the other arteries of the body, the 

 coronary arteries would therefore fill only during diastole, and this increased fulness 

 of the vessels in the heart walls during diastole would assist the ventricle to dilate. 

 This, however, is incorrect ; the valves do not cover the mouths of the arteries ; and 

 at the beginning of systole the velocity and pressure in the coronary arteries 

 increase ; but later on during systole the ventricular wall is so strongly contracted 

 that the muscular tension becomes greater than the coronary pressure, and so the 

 coronary arteries and their branches are compressed, and the blood clriveri back 

 into the aorta ; the coronary arteries are then again filled with the commencing 

 diastole. Self-steering action of the heart therefore exists, but it is brought about in 

 a different way from what Briicke supposed. 



Cardiographs. 



A cardiograph is an instrument for obtaining a graphic record 

 of the heart's movements. In animals the heart may be exposed, 



