EVENTS DURING A CARDIAC CYCLE. 



77 



(3.) The blood is driven into the relaxed ventricles, which are con- 

 siderably distended thereby. 



The contraction of the auricles is followed by 



(a.) A slight stagnation of the blood in the large venous trunks, as 

 can be easily observed in a rabbit after division of the pectoral muscles 

 so as to expose the junction of the jugular with the subclavian vein. 

 There is no proper regurgitation of the blood, but only a partial 

 interruption of the inflow into the auricles, because, as already men- 

 tioned, the mouths of the veins are contracted, and because the 

 pressure in the superior vena cava and in the pulmonary veins soon 

 holds in equilibrium any reflux of blood; and lastly, because any reflux 



Gypsuin cast of the ventricles of the human heart viewed from behind and above; 

 the walls have been removed, and only the fibrous rings and the auriculo- 

 ventricular valves are retained L, left, R, right ventricle; S, position of 

 septum; F, left fibrous ring, with mitral valve closed; D, right fibrous ring, 

 with tricuspid closed ; A, aorta, with the left (Ci) and right (C) coronary 

 arteries ; S, siuus of valsalva ; P, pulmonary artery. 



