166 



UNCONSCIOUS NERVOUS OPERATIONS 



230. Action of the Heart in the Circulation (Fig. 96). In 

 the beating of the heart, the contraction of the muscular 

 4 walls commences at the 



mouths of the great 

 veins in the auricles, 

 runs through the two 

 auricles and then over 

 the two ventricles to- 

 gether, the auricles be- 

 ginning to dilate as the 

 ventricles begin to con- 

 tract. Then there is 

 an instant's pause, when 

 neither set of muscles 

 are contracting, but the 

 whole heart is expand- 

 ing, and its walls are 

 soft and flabby. 



The impulse from the 

 heart's contraction is 

 felt in the arteries of 

 the wrist, the temples, 

 and some other parts of 

 the body, and is called 

 the pulse. 



During the pause the 

 relaxed walls of the 

 heart yield to the blood 

 which flows into the 

 auricles from the pul- 



Fig. 96. Diagrams illustrating the ac- monary veins and the 

 tlooi of the valves of the heart. venffi ^^ 



A during the filling of the right ventricle. . 



11 during the contraction of the ventricle. lunar valves 



, 

 at tlie 



