192 DR D. NOEL PATON ON THE 



" 4°. La contraction des muscles papillaires a pour effet la tension des cordages 

 tendineux et l'abaissement des valvules. Cet effet se produit malgre le raccourcissement 

 systolique du diametre longitudinal des ventricules, admis par la plupart des auteurs. 



" 5°. Les muscles papillaires du ventricule gauche sont disposes de facon a. s'emboiter 

 l'nn dans l'autre et a combler la portion gauche de la cavitd ventriculaire. En se 

 contractant, ils attirent a gauche les deux valves de la mitrale, qu'ils appliquent Tune sur 

 L'autre et contre la paroi du ventricule. La valve droite joue le role essentiel dans 

 l'occlusion de l'orifice auriculo-ventriculaire ; mais la valve gauche n'est pas inutile, non 

 plus que les deux languettes valvulaires accessoires. 



" 6°. Le mode de resserrement du ventricule droit differe notablement de celui du 

 ventricule gauche, ce qui a necessite des dispositions particulieres dans la valvule 

 tricuspide. 



"7°. Les muscles papillaires du ventricule droit, en se contractant, appliquent et etalent 

 les valves de la tricuspide a, la surface de la cloison. La forme convexe de cette derniere 

 rend compte de l'existence de trois valves dans le cceur droit. 



"8°. II y a dans la paroi ventriculaire droite un gros faisceau musculaire dont Taction 

 supplee celle de la pression sanguine, si considerable dans le ventricule gauche. Ce 

 faisceau musculaire est l'analogue du demi-sphincter qui remplace la valvule tricuspide 

 dans le cceur des oiseaux." 



These conclusions have been arrived at by reasoning from the anatomy of the heart 

 as demonstrated in the ordinary methods of dissection, aud from experiments on the dead 

 and flaccid heart, but not from any direct observations. 



The adoption of this view as to the mode of action of the auriculo- ventricular valves 

 will modify our conception of the mechanism of regurgitation. 



It has always been difficult to understand how, with even a small degree of dilatation 

 in cardiac debility, regurgitant murmurs are produced. 



The valves are so large in relationship to the orifices (Hermann's Handbuch der 

 PJiysiologie, Bd. vi. S. 161) that one should expect that even though the dilatation 

 were very considerable, if the valves assumed the horizontal position usually described, 

 the occlusion would be complete. 



When, however, we consider the importance of the action of the papillary muscles 

 in the closure of the valves, and when we remember that their vascular supply is a 

 terminal one, and that they are therefore early the seat of degenerative changes (Fenwick 

 and Overend, loc. cit.), and when we recall the fact that in abnormal conditions of the 

 heart these muscles do not act so promptly as they should do, we can readily see that 

 the valves will frequently not be closed before auricular dilatation commences, and that 

 thus a back flow of blood will occur. This will be specially apt to happen on the right 

 side of the heart. 



Again, to close the orifices in the manner we have described requires valves of con- 

 siderably greater size than would be necessary to occlude the orifice in the horizontal 



