i 7 6 



THE CIRCULATION OF THE BLOOD 



somewhat inconstant in appearance, but has been found to be equal to as 

 much as 20 mm. of mercury, and is said to be quite independent of the 

 aspiratory power of the thorax itself, which will be described in a later 

 chapter. The ventricles now remain in a state of relaxation or rest until 

 the next systole begins. 



The duration of the ventricular systole and the diastole has been variously 

 estimated. A computation of the time of these two phases, for man, in 

 figure 153, reproduced from Hiirthle, gives for the systole 0.38 of a second 

 and for the diastole 0.4 of a second, with a total of o. 78 of a second. This 

 is equivalent to a rate of 77 per minute. Variation in the time of the systole 

 and the diastole of the ventricle falls chiefly on the pause of the diastole. 



The ventricles undergo little or no change of shape in the unopened chest. 

 At the moment in the systole when the ventricles begin to discharge their 



Left anterior cusp of 

 pulmonary valve 



Left posterior cusp of 

 pulmonary valve 



Left posterior cusp of 



aortic valve 

 Left coronary artery 



Anterior cusp of 

 mitral valve 



Posterior cusp of 

 mitral valve 



Left ventricle 



~~ Conus arteriosus 



Right anterior cusp 

 of pulmonary valve 



Right coronary 

 artery 



Anterior cusp of 

 aortic valve 



Right posterior cusp 



of aortic valve 

 Anterior (infundibu- 

 lar) cusp of tricuspid 



valve 



Right (marginal) 

 cusp of tricuspid 



valve 



Posterior (septal) 



cusp of tricuspid 



valve 



Right ventricle 



FIG. 151. The Bases of the Ventricles of the Heart, showing the auriculo- ventricular, 

 aortic, and pulmonary orifices and their valves. (Cunningham.) 



contents into the aorta and pulmonary arteries, respectively, there is a sharp 

 decrease in size of the ventricles. This decrease takes place in all 

 dimensions. 



Action of the Valves. The Tricuspid Valve. During the diastole 

 of both auricles and ventricles blood flows directly through the auricles into 

 the ventricles, the auricles during this period acting as continuations of the 

 large veins which empty into them. At the end of the period the ventricle 

 on each side has already been filled and distended by the pressure of blood 

 from the veins. The systole of the auricle completes this filling and slightly 

 overdistends the ventricle. When the force of the auricular contraction is 



