276 SIXTH REPORT — 1836. 



suppose that the contractions of the former as of the latter class 

 of fleshy columns are synchronous with those of the general 

 mass. In the second place it is to be considered that if the 

 papillary muscles were not in a state of contraction during the 

 whole of the ventricular systole, the valves to which they are 

 attached would be driven up by the impulse of the blood into 

 the auriculo-ventricular openings, and thus become unfitted for 

 their of&ce, as is seen in the dead heart, in which a stream of water 

 injected into either ventricle by its artery, drives the valves 

 towards the auricle until the water escapes between their edges. 

 It is to be observed also that in many quadrupeds, and to a cer- 

 tain extent in the human subject, some of the tendinous cords 

 attached to a valve are connected to papillary muscles, while the 

 remainder are inserted directly into the surface of the ventricle : 

 but it cannot be supposed that the former set of tendons are at 

 rest while the latter are acted upon by the general ventricular 

 contraction. 



To the solution of the second question a consideration of the 

 manner in which the mitral and tricuspid valves are connected 

 with their respective papillary muscles, and of the relation of 

 these to the rest of the substance of the heart is necessary. 

 Each of these valves may be regarded as a portion of a hollow 

 membranous cylinder, attached by one edge around the auriculo- 

 ventricular opening, the other edge projecting into the ventricle 

 and connected to certain of the tendinous cords. The greater 

 number of these, however, are joined to the valve, not at its edge, 

 but at various points of its ventricular surface. The ventricular, 

 or moveable edges of those valves are extremely irregular in their 

 outline, being deeply notched in some parts and projecting in 

 others ; but as to their mode of operation each valve may be con- 

 sidered as consisting of two flaps, a larger and a smaller one, by 

 the application of which to each other during the ventricular 

 systole the blood is prevented from regurgitating into the auricles. 

 The large flap of the mitral valve is placed between the orifice 

 of the aorta and the left auriculo-ventricular opening, nearly in 

 a horizontal plane, the heart being supposed to be in its natural 

 position, and the person in the upright posture, and may bo 

 described in reference to the smaller flap as superior, somewhat 

 anterior, and a little to the right side. The smaller flap is placed 

 opposite to the larger, and is, with regard to it inferior, some- 

 what posterior and a little to the left. When these flaps are in 

 opposition during the systole of the ventricle, the line of their 

 contact is of a somewhat semilunar form, and in the transverse 

 direction. 



The larger flap of the tricuspid valve is attached to that part of 



