ON THE MOTIONS AND SOUNDS OP THE HEART. 279 



It is also an erroneous assumption that the valves are ren- 

 dered tense by the action of the papillary muscles, unaided by 

 the influence of the blood upon the surfaces of the valves : for, 

 were it true, by the time when the contraction of these muscles 

 is at its greatest, and for some time previous, the valves would 

 be held by them in an open state, as has just been proved ; and 

 thus during a portion of the systole, towards its end, the closing 

 of the passages into the auricles would be rendered incomplete. 

 It is accordingly inconsistent with the functions of the heart 

 that the papillary muscles, in their state of greatest contraction, 

 should render the valves tense : it follows that they cannot ren- 

 der them tense at any previous stage of contraction. 



The valves are closed by the impulse communicated to them 

 through the blood at the commencement of the systole; and 

 are prevented from separating during its continuance by the 

 same cause. The papillary muscles have for their office to re- 

 gulate the position of the valves, and to prevent them from 

 being driven so far towards the auricles as to render incomplete 

 the closing of their orifices. It does not appear that the action 

 of the papillary muscles is at all necessary for the removal of 

 the flaps from the sides of the ventricles, in order that the blood 

 may be admitted between them at the commencement of the 

 systole : for in the dead heart, if water be injected into either 

 ventricle, through its corresponding artery, or through a hole 

 made in its apex, it never fails to float the valves towards the 

 auricles, and to bring their respective flaps into close contact. 

 If force be used in this experiment the valves are driven into 

 the auriculo-ventricular openings, and the water escapes between 

 their edges. In this experiment it is seen also that the tricus- 

 pid valve performs its office as completely as the mitral, op- 

 posing a perfect obstacle to the flow of blood until force is em- 

 ployed. 



It is probable that in the living heart the valves are not 

 applied close to the sides of the ventricles, when these are in their 

 diastole, and full of blood ; but that an interval exists between 

 them occupied by this fluid. The central position of the papil- 

 lary muscles of the larger flaps, and the shortness of their ten- 

 dons are favourable to this supposition ; and, in the right ven- 

 tricle, the mode in which the smaller flap is connected to the 

 septum, by tendons inserted directly, and without papillary 

 muscles, requires for the closing of this portion of the valve, 

 that the blood should have insinuated itself between it and the 

 adjacent surface, previously to the commencement of the systole^ 

 inasmuch as the mei'e muscular contraction of the ventricle is 



