PHYSIOLOGY OF THE HEART.
Made of action of the valves of the heart.— While the blood is rushing through the auri culo-ventricular openings during the contrac tion of the auricles, the lips of the mitral and tricuspid valves are separated from each other and thrown outwards from the axis of the opening, and the larger lip of both is at this time carried towards the arterial orifices. It has generally been supposed that the mitral and tricuspid valves are, during the systole of the ventricles, passively floated up towards, and obstruct the auriculo-ventricular orifices so as to prevent the free regurgitation of the blood into the auricles; and that the use of the corder tendinere is merely to limit the movements of the valves,—to permit them to be raised suffi ciently to close the orifices, but at the same time to provide against the otherwise unavoid ably fatal consequences that would result from these unresisting valves being carried through into the auricles by the current of blood. Mayo, Bouillaud, and others have, however, main tained that the lips of these valves are not approximated in the mechanical manner just stated, but by the contraction of the musculi papillares of which the cordm tendinem are the proper tendons. As the musculi papillares contract along with the other fibres of the ven tricles, the lips of the valves are drawn towards the axis of the opening, and are closely applied to each other, forming a kind of cone, the apex of which projects downwards into the ven tricles. It is from the adoption of these views that Bouillaud proposes to call these musculi papillares, the tensor, elevator, or adductor muscles of the valves. That the lips of the valves are approximated in this manner appears to me to be the much more probable opinion; for when we examine the uniform position and course of the museuli papillares and chord tendinew, more particularly those of the left ventricle ; that the chords tendinere pass from each museulus papillaris to both lips of the mitral valve, occasionally crossing each other ; and that the posterior or smaller lip, though it may be drawn inwards so as to meet the larger and more moveable, is so bound down as to be scarcely capable in most cases of being floated up on a level with the orifice; and further, when we also remember that the mus culi papillares contract at the same time with the other fibres of the heart, we can scarcely resist coming to this conclusion. Besides, if
the lips of the valves were floated up to the orifice, a greater quantiti of blood would regur gitate into the auricles during the systole of the ventricle than in all likelihood takes place; for as the lips of the valve must be widely separated from each other when the systole commences, it is evident that a less quantity of blood must have passed through the orifice before the lips are sufficiently approximated to obstruct its further passage when these are assisted by an active force, than when they are merely passively brought together by the cur rent of blond passing in that direction. It has, however, been supposed that the museuli papillares do not contract with the other fibres of the ventricles. hailer states* that on laying open the heart he has seen the muscles of the valves contract during the systole of the heart. It may be objected to this experiment that the unusual stimulus applied to the heart in cutting its fibres across may have deranged the usual order of its contractions. I have repeatedly opened the heart in rabbits and waited until its contractions had ceased, and on renewing its movements by irritating the inner surface at a distance from the cut edges, I have observed that the eolumnre carnet': acted simultaneously with the other muscular fibres of the heart.f I was also satisfied that the musculi papillares were proportionally more shortened during their contraction than the heart itself taken as a whole, which is nothing more than what we would expect when we remember that the fibres of the museuli papillares are so far free and run longitudinally, while by far the greater part of the other fibres run in a spiral manner.