!faller, in relating his observations on the contraction of the musculi papillares, makes another statement, which, however, is decidedly adverse to this opinion. The chords tendinem appeared to him to be relaxed during the con traction of the museuli papillares.
It is difficult to make satisfactory observa tions upon the effects of the contractions of the musculi papillares upon the tension of the chords tendinem. In several animals upon which we attempted to ascertain this, it was only when the heart was acting languidly that we could observe what was likely to be the effect of the contraction of the musculi papil lares on the chordal tendinem when they were placed as far as possible in their natural rela tion to each other. We could never observe that they contracted sufficiently to move the valves, but they certainly rendered some of the chords tendinem more tense. When, however, we take into account, that in an experiment of this kind, the valves arc not thrown out widely from the orifices of the auriculo-ventrieular orifices, the ventricle is not distended with blood, the chords tendinem consequently not put so far on the stretch as occurs at the com mencement of the systole, and that the con tractions of the museuli papillares are languid, we can easily perceive how, in the natural systole of the heart, these contractions of the museuli papillares should be sufficient to move the valves inwards, though not to such an extent as to apply them closely to each other. The con traction of these musculi papillares apparently sets the valves in motion, and they are subse quently applied to each other by the currents of blood. It may be supposed that if the con traction of these =scull papillares can render the chord tendinem sufficiently tense to move the valves, this would prevent the subsequent elevation of them to obstruct the auriculo ventricular opening. We believe, however, that it is only at the commencement of the systole that they are sufficiently tense to move the valves, for as the contraction proceeds the capacity of the heart is so much diminished, both in its transverse and longitudinal dimen sions, that they become relaxed. Besides, if
we could suppose that these musculi papillares are capable of contracting through a sufficient space to draw the valves together, this would be all that is necessary to prevent the regurgita tion of the blood through the auriculo-ventri cular opening.* So convinced, indeed, were the older anato mists and physiologists that the chords tendinem are relaxed during the systole of the heart, and of the necessity of an accompanying diminution of the length of the ventricles themselves to effect this, that this argument adduced by Bassuel appears to have been principally instrumental in deciding the once keenly controverted ques tion whether or not the heart was elongated during its contraction.t It may be supposed that the relative size of the auriculo-ventricular orifices to the length of the lips of the valves would not admit of their apices being brought together in the form of a cone as described, but it must be remembered that from the course of the muscular fibres in the immediate neighbourhood of those open ings, their areas must be diminished during the systole of the heart. There is at least one thing certain connected with the action of these valves, viz. that the contraction of the musculi papillares can never cause the valves to strike the inner surface of the ventricle and produce a sound as has been supposed.
The manner in which the semilunar valves at the origin of the aorta and pulmonary artery perform their office is entirely mechanical and easily understood. During the systole of the heart they are thrown outwards from the axes of these vessels; but during its diastole, when part of the blood driven into the artery would fall back into the ventricles, these valves are thrown inwards and obstruct completely the whole calibre of the arteries. In all probability the sinuses of Valsalva placed behind these valves contain a certain quantity of blood even during the systole of the heart, and this re acting upon the valves through the agency of the elasticity of the arteries brought into opera tion at the termination of the systole, materially assists in producing the more rapid and certain action of the valves.