796 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION, 



when the ventricles are full of blood and the auriculo-ventricular orifices widest,— 

 it is scarcely possible that it could keep them closed towards the end of the 

 systole, when the auriculo-ventricular orifices are greatly diminished in size and the 

 blood itself all but ejected. A regulating and motor power, therefore, in addition 

 to the blood, for adapting the different portions of the segments of the valves to 

 the varying conditions of the auriculo-ventricular orifices and cavities during 

 the systole, seems requisite. Such a power, in my opinion, resides in the conical- 

 shaped spiral musculi papillares with their proper tendons — the chordse tendinese. 



That the theory which ascribes the closing of the auriculo-ventricular valves, 

 entirely " to the contraction of the musculi papillares," is likewise of itself in- 

 sufficient, appears for the following reasons : — 



1^^, If the valves which, at the commencement of the ventricular diastole, hang 

 free in the ventricular cavities, and are undoubtedly floated mechanically upwards, 

 so as to have their edges approximated by the blood towards the termination of 

 that act, were dragged upon at the instant of contraction from above downwards, 

 or in an opposite direction to that in which the force by which they were brought 

 together acts, the segments of the valves, instead of being further approxi- 

 mated, would inevitably be drawn asunder, and regurgitation to a fatal extent 

 supervene. 



2d, By such an arrangement as Dr Halford has satisfactorily shown, the 

 cavities of the ventricles would not only be materially diminished at a very in- 

 convenient time,* but a certain amount of the force required for the expulsion of 

 the blood from the ventricular cavities, would be expended in closing the valves. 

 While, therefore, it seems essential for the apj roximation of the auriculo-ventri- 

 cular valves, that they should first ascend with the ascending columns of blood 

 occasioned by the injection of the ventricles by the auricles, so as to have their 

 margins gradually and accurately approximated, in order that when the contrac- 

 tion of the ventricles takes place, they may be instantly closed,-|- thereby effect- 

 ually preventing regurgitation ; so, for their continued closure, it seems necessary, 



* Dr Halford states lils belief, " that tlie segments of the valves are forced even beyond the 

 level of the auriculo-ventricular orifices, and in this way become convex towards the auricles, and 

 deeply concave towards the ventricles." In his zeal for the enlarged accommodation of the ventricles, 

 he forgets that the auricles are equally entitled to consideration, and that it is unfair to give to the 

 one and take from the other ; for if, as he argues, the segments of the valves form a convex partition, 

 whose convexity throughout the entire systole of the ventricle points in the direction of the auricles, 

 the space beyond the level of the orifices is appropriated from the auricles without compensation. As, 

 however, such an arrangement could not fail materially to inconvenience the auricles, when they 

 are fullest of blood, we naturally turn to the ventricles for redress. The additional space required 

 is, as I have already shown, supplied by the descent of the segments of the bicuspid and tricuspid 

 valves towards the end of the systole when the ventricles are almost drained of blood. — On the 

 Time and Manner of Closure of the Auriculo-ventricular Valves. Churchill, London, 1861. 



f The mai-gins of the segments of the valves at the end of the ventricular diastole are so close 

 as to be nearly in contact. The slightest amount of pressure, therefore, sufiices for the instantaneous 

 closure. As, moreover, regurgitation is prevented in proportion to the rapidity with which the 

 closure is effected, the efficiency of this ari-angement is at once apparent. 



