THE HEART. 327 



the dog, and, fastening it upon a table by needles passed through its base, 

 found the ventricles shortened in contraction ; and obtained the same 

 result, in another experiment, by pinning the heart, in the chest of the 

 living animal, to a thin board placed underneath. On the other hand, 

 Drs. Pennock and Moore, who performed a series of very careful experi- 

 ments upon the action of the heart in sheep, calves, and horses, 1 observed 

 an elongation of the organ at the time of the ventricular systole. They 

 operated by stunning the animals with a blow upon the head, opening 

 the chest, and keeping up artificial respiration, and they were able to 

 measure the extent of elongation by means of a shoemaker's rule applied 

 to the heart. 



In our own observations on this point, many times repeated, we have 

 always seen reason to believe that the heart actually elongates in the 

 ventricular systole, and that it is not simply thrown forward by an im- 

 pulse of recoil. The appearances presented, when viewing the front of 

 the mammalian heart, as it lies in its natural position in the chest, are 

 somewhat complicated. The anterior surface of the organ is mainly 

 occupied by the right ventricle and especially by that portion of it 

 known as the conus arteriosus. This is in reality a vaulted channel 

 running obliquely over the front of the heart, from right to left and from 

 below upward, toward the origin of the pulmonary artery. Its muscular 

 fibres, on the other hand, run directly across it and at right angles to 

 the axis of its cavity, namely, from right to left and from above down- 

 ward, constituting the most superficial fibres of the heart in this situa- 

 tion. At the time of ventricular systole, these fibres contract across the 

 line of the conus arteriosus, become thickened and more prominent and 

 approximate the base of the heart and the lower -border of the conus 

 arteriosus toward each other. 



But the right ventricle constitutes a comparatively small portion of 

 the heart. The greater part of its mass is formed by the thick walls of 

 the left ventricle, which occupies a posterior position, and is not fully 

 seen in a front view of the organ. If the heart be tilted up and viewed 

 from its posterior surface, at every contraction its sides will be seen to 

 approximate and its point to elongate ; in other words, its transverse 

 diameter diminishes, while its longitudinal diameter increases. Its base 

 may be firmly held by the fingers placed upon the large vessels, -while 

 this change of form of the organ is observed. Even in an anterior view, 

 with the whole heart securely held in this position, according to our 

 observations, the apex, at each systole, will rise toward an ivory rod 

 placed horizontally above it, and will recede in the same degree at each 

 diastole. 



If this be true, the explanation of the ventricular elongation is readily 

 found in the arrangement of the muscular fibres of the left ventricle. 

 The left ventricle preponderates so much in mass over the other parts of 

 the organ, that its changes of figure determine those of the entire heart. 



1 Philadelphia Medical Examiner, 1839, No. 44. 



