512 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



apparatus acts as a sort of hollow piston, which penetrates the ventricle 

 and comes into close contact with its walls, and thus the ventricle (Figs. 

 20? and 208) empties itself completely, the contact becoming perfect 

 between its sides and the auricular prolongation. 



" The result of this mechanism, which is so simple, and yet so gen- 

 erally misunderstood, is that no reflux of blood into the auricle can take 

 place ; the auricle, even by means of the mechanism which we have de- 

 scribed, exercises a sort of suction upon the venous blood, its cavity being 



Fig. 208.— Heart of A Cow, with Left Auricle and Ventricle Laid 

 Open. (Miiller.) 

 a, root of the aorta ; b, spaces in the wall of the auricle : c c, orifices of the pulmonary veins : I J, pul- 

 monary veins ; p p, papillary muscles ; q ql, columnar carnie ; t, auricular trabecular : A, orifice of the 

 aorta; K, left ventricle ; S, septum; V, left auricle ; W, lateral wall of left ventricle ; 1, 2, leaflets of the 

 mitral valve. 



continued so far into the ventricle. We see, also, that when the ventricular 

 systole is complete, the lengthened tube, the hollow cone which unites 

 the ventricle and the auricle, is full of blood, and that a slight and rapid 

 contraction of the auricle is sufficient to drive this blood into the ven- 

 tricle and fill it. 



" Nearly all the standard works admit without discussion the theory 

 of the occlusion of the auriculo-ventricular orifices by the simple mech- 



