ACTION OF THE VALYES OF THE MAMMALIAN HEART. 



189 



indicate an objection to this theory. Unless the papillary muscles act almost synchro- 

 nously with the rest of the muscle substance, it is not easy to conceive that the valves 

 could be closed in the manner described. 



While fully recognising the value of their work, I do not think that they have con- 

 clusively proved their contention that the contraction of the papillary muscles is later 

 than that of the ventricular wall. 



The papillary muscles are nothing more or less than special developments of the 

 trabecular tissue of the foetal heart from which the columnse carnese also spring. They 

 are, in fact, simply columnse carnese ; and all gradations may be traced from the large 

 papillary muscles through the small muscular 

 prominences giving origin to a single cord, to 

 the proper muscular substance of the heart. 

 In the left ventricle of the rat the two papillary 

 muscles are replaced by two columnse carnese, 

 from the sides of which the chordae tendinese 

 spring. Which of these papillary muscles 

 contracts after the heart substance, and which 

 contract with it ? It would indeed be curious 

 to find a delay in the contraction of certain of 

 these muscles and not in others. 



But a careful study of their work by no 

 means bears out their conclusions as to the 

 late contraction of these muscles. Undoubtedly 

 these structures shorten greatly and still further 



pull down the valves at a period later than the commencement of the contraction of the 

 ventricles, just at the time when the blood is expelled into the arteries. Roy and Ad ami 

 look upon this as the cause of the expulsion of blood ; but it is much more probably the 

 result. Until the semilunar valves are opened, and the blood begins to leave the ven- 

 tricles, the papillary muscles may enter into a state of contraction ; they may approxi- 

 mate the cusps of the valves, but they cannot pull these down upon the ventricular con- 

 tents. As the blood, however, passes out, these structures can shorten ; and their 

 shortening may influence the long and transverse diameter of the ventricles, as described 

 by these authors. 



Farther, as a result of their researches, Fenwick and Overend (Brit. Med. Journal, 

 vol. i. p. 1118, 1891) conclude that it is "extremely probable that the shortening of the 

 two muscles (i.e., the wall muscles and papillary muscles) under normal circumstances is 

 practically simultaneous." 



A review of the older work upon this subject — which undoubtedly points to the 

 simultaneous action of papillary muscles and ventricular wall — will be found in a paper 

 by See (see p. 191). 



So far as our evidence at present goes, we must conclude that the papillary muscles 



