OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 791 



at the margins and towards the apices are short, and in some instances as delicate 

 as hairs, it follows that every part of the valves in question, bears a graduated 

 relation to, and is under the control and domination of, the conical-shaped spiral 

 musculi papillares, whose power to contract is now well established.* It is 

 therefore my impression, and my belief is shared by others, that the chordae ten- 

 dinese ought to be regarded as the satellites of the actively contracting musculi 

 papillares, under whose guidance they have to perform, not only a very important 

 but a very delicate function, and one which could not by any possibility, be 

 accomplished by a simply mechanical arrangement. 



The Mitral and Tricuspid Valves of the Mammal in Action. 



The theories which have long divided the attention of physiologists with 

 regard to the action of the mitral and tricuspid f alves, are two in number ; one 

 sect maintaining, that the valves m^e acted upon mechanicalli/ by the Hood, as if 

 they were composed of inanimate matter ; the other believing, that they form 

 imi't of a living system, their movements being traceable to their connection 

 with the musculi papillares, which are actively contracting structures. 



In the mechanical theory, the segments of the valves are supposed to be j!?«s- 

 sively floated up by the blood, which acts upon them from beneath during the 

 systole, and brings their edges or free margins into such accurate apposition as 

 enables the segments completely to occlude the auriculo-ventricular orifices. In 

 these movements the musculi 2)CLpill<^res and carnew columnw are said to take no 

 part : the chordae tendinese acting mechanically, like so many stays, to prevent 

 eversion of the segments in the direction of the auricles. 



In the vital theory, on the other hand, the segments of the valves are sup- 

 posed to be from the first under the contj'ol of the musculi papillares ; these 

 structures, by contracting, drawing the lips or free margins of the segments closely 

 together in the axis of the auriculo-ventricular openings, to form two impervious 

 cones, the apices of which project downwards into the cavities of the ventricles. 



In these movements, it is maintained, the Mood takes no part, the chordae ten- 

 dinese, which are regarded as the proper tendons of the musculi papillares, acting 

 as adjusters or adapters of the segments ;-f a function which their varying length 

 and strength readily enables them to perform. 



I need scarcely add, that these theories are diametrically opposed to each 



* Dr John Reid states from experiment, that the carneae columnse. act simultaneously witli the 

 other muscular fibres of the heart, and that the musculi papillares are proportionally more shortened 

 durmg their contraction than the heart itself taken as a whole. He attributes this to the more 

 vertical direction of the musculi papillares, and to their being free towards the base and in the direc- 

 tion of the ventricular cavities. — Cyc. of Anat. and Fhy., art. " Heart," p. 601. London, 1839. 



•f* In one specimen which I dissected, the chordae tendineoe contained a large amount of muscular 

 fibre, and were so thickened as to resemble rudimentary musculi papillares. 



