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TEXT-BOOK OF PHYSIOLOGY. 



size of its cavities and in that of the blood-vessels arising from them, and 

 the relative position of the valves during systole and diastole are shown in 

 Fig. 126. 



Relative Functions of Auricles and Ventricles. Though both 

 auricles and ventricles are essential to the continuous movement of blood, 

 they possess unequal values in this respect. The passage of the blood 

 through the pulmonary and systemic vessels is accomplished by the driving 

 power of the right and left ventricles respectively, aided, however, by minor 

 extra-cardiac forces. They may be regarded therefore as force-pumps. 



If the heart consisted of ventricles only, the flow of blood from the venae 

 cavae and pulmonary veins would be temporarily arrested during their systole 



S.a.-D.v. 



D.a.-S.v. 



FIG. 126. DIAGRAMMATIC REPRESENTATION OF THE AURICULAR SYSTOLE, S.a., WITH THE 

 VENTRICULAR DIASTOLE, D. v., AND OF THE AURICULAR DIASTOLE, D. a., WITH THE VENTRICULAR 

 SYSTOLE, S.v. C.s. and C.i. Superior and inferior cavae; A.d. (atrium dextrum) right auricle; 

 A.s., (atrium sinistrum) left auricle; V.d. (ventriculus dexter) right ventricle; V.s. (ventriculus 

 sinister) left ventricle; P. pulmonary artery; A. aorta; P.P. papillary muscles. (Landois.) 



and their subsequent refilling delayed. This is obviated, however, by the 

 addition of the auricles; for during the ventricular systole the blood continues 

 to flow into the auricles, in which it is temporarily stored until the ventricular 

 relaxation sets in. With this event the accumulated blood passes into the 

 ventricles, which are thus practically filled before the auricular systole occurs 

 by which the filling is completed. By this means there is no delay in the 

 filling of the ventricles, and hence their effective working as force-pumps is 

 more readily secured. The auricles may therefore be regarded as feed- 

 pumps. For this reason it is probable, notwithstanding the contraction of 

 the circular muscle-fibers at the terminations of the venous system, that the 

 flow of blood into the auricles is never entirely arrested. Regurgitation in 



