510 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



The leaflets of these valves again subdivide into numerous tendinous 

 filaments which are inserted in the papillary muscles of the heart (Figs. 

 205 and 206). The tendinous threads which arise in the papillary muscles 

 and are inserted in the valve are not in connection solely with the free 

 border of the latter, but the entire surface of the valve, which is directed 

 toward the walls of the ventricle, offers points of insertion for these 

 tendons (Figs. 207 and 208). 



Numerous theories have been proposed to explain the manner in 

 which the auriculo-ventricular valves prevent, in the systole of the ven- 



FIG. 206. HEART OF THE HORSE, SEEN FROM THE LEFT SIDE, THE LEFT 

 AURICLE AND LEFT VENTRICLE BEING LAID OPEN. (Muller.) 



I V, left auricle : IK, left ventric'e; r K, right ventricle; 1, trabeculae in left auricle; 2, coronary 

 fissure, with its artery and vein ; 3, pulmonary artery ; 4, anterior aorta ; 5, posterior aorta : 6, left longi- 

 tudinal furrow ; 7. left coronary artery; 8, coronary 'vein ; 9, columnar carnae ; 10 10', papillary muscles; 

 11 11', chordae tendinae; 12 12', mitral valve. 



tricle, regurgitation of blood into the auricles. These may be classified 

 into two different groups. 



According to the one, the occlusion is purely passive, and is pro- 

 duced by the pressure of the blood behind the valves, causing their 

 ascent, and so occluding the orifice between the ventricles and auricles. 

 In this view of their action, the papillary muscles have for their sole 

 function the regulation of the situation of the valves, and, consequently, 



