9 8 



THE MOVEMENTS OF THE HEART. 



2. At the same time the blood presses against the under surface 

 of the auriculo- ventricular valves, the inverted margins of which 

 interdigitate and become hermetically applied to one another (Fig. 26). 

 The valve-leaflets are prevented from being forced back into the 

 auricular cavity, because the tendinous cords hold their under surface 

 and margins firmly like an inflated sail. The approximation of the 

 edges of adjacent valves is favored further by the circumstance 

 that the tendinous fibers always pass from one papillary muscle to 

 the edges of two opposed valves. To the extent that the lower ven- 



FIG. 26. Plaster Cast of the Ventricles of the Human Heart, Viewed from Behind and Above. The walls are 

 removed, only the fibrous rings and the auriculo-ventricular valves being retained: L, left; R, right ventricle; 

 S, situation of the septum; F, left fibrous ring, with closed mitral valve; D, right fibrous ring, with closed tri- 

 cuspid valve; A, aorta, with the left (ci) and the right (c) coronary artery; 5, sinus of Valsalva; P, pul- 

 monary artery. 



tricular wall approaches the valves during contraction and thus might 

 render possible a bulging backward of the valves into the auricle, com- 

 pensation is provided by the shortening of the papillary muscles and 

 of the large muscle-containing tendinous cords themselves. The valves 

 when closed present an approximately horizontal surface. There re- 

 mains, therefore, in the ventricles, even at the height of contraction, 

 always a remnant of blood, the so-called residual blood. 



3. When the pressure in the ventricle exceeds that in the arterial 



