THE CORONARY VESSELS. 93 



THE CORONARY VESSELS; AUTOMATIC REGULATION, NUTRI- 

 TION, AND ISOLATION OF THE HEART. 



With reference to the origin of the coronary arteries the question at 

 once arises whether the orifices of these vessels are closed by the eleva- 

 tion of the semilunar valves during systole as a result of the application 

 of the valve-leaflets to the walls of the vessels or whether such occlusion 

 does not take place. 



Anatomical. The two coronary arteries arise from the region of the sinus 

 of Valsalva. The point of origin varies: (i) It is either within the concavity of 

 the sinus; or (2) the mouths of the vessels are not completely within the range 

 of the margin of the valve, and this is frequently the case with the left coronary 

 of man and the ox; or (3) the orifices project beyond the margins of the valve 

 (this is rare). These findings alone make it improbable that closure of the 

 mouths of the coronary arteries by the semilunar valves during ventricular systole 

 is a constant physiological phenomenon. 



AUTOMATIC REGULATION OF THE HEART. 



According to Briicke the openings of the coronary arteries are 

 covered by the semilunar valves during systole, so that they can be 

 filled only during diastole. The advantage of this arrangement resides 

 in the fact that (a) the diastolic distention of the ventricular vessels 

 stretches the muscular fibers of the ventricular wall and thus corre- 

 spondingly dilates the ventricle for the reception of the blood that 

 pours in from the auricle during diastole. (6) On the other hand, 

 the systolic distention of the coronary arteries would be useless because 

 the dilatation of the ventricular wall (due to the distention of the 

 arteries already mentioned) would resist the systolic contraction, 

 and because the systolic distention of the coronary arteries and the 

 expulsion of the blood from them would unnecessarily diminish the 

 power of the ventricle. Accordingly, the diastolic distention of the 

 coronary arteries* would be most consistent with the mechanical 

 conditions present. This mechanism Briicke has designated the "auto- 

 matic regulation of the heart." 



FIG. 24. Semilunar Valves, Closed. Semilunar Valves, Opened. 



This theory and its underlying principles are untenable, for 



1. The filling under high pressure of the coronary arteries of a dead heart 

 not only is followed by no dilatation, but actually causes a contraction of the 

 cavity of the ventricle. 



2. The chief branches of the coronary arteries lie in the sulci of the heart 

 embedded in the loose subpericardial fatty tissue, where their dilatation and con- 

 traction could scarcely have any effect upon the size of the cavities of the heart. 



3. Brown-S6quard found in animals and v. Ziemssen in a woman with a large 

 deficiency in the wall of the left thorax that the coronary pulse was synchronous 

 with that in the pulmonary artery. Newell-Martin and S'edgwick, by introducing 

 manometers into the coronary and carotid arteries of a large dog, obtained simul- 



