43S 



ANIMAL MECHANICS. 



complete circumference, the transverse components of the 

 force of contraction will equilibrate each other, and thus no 

 motion of rotation is given to the heart by these fibres ; on 

 the other hand, the transverse components of the force of 

 contraction of the proper fibres are unsymmetrical, and they 

 will give a resultant twisting motion to the cavity of the ven- 

 tricle, the effect of which will be, to wring out completely 

 every drop of blood from the ventricle at the close of the 

 systole. 



Having ascertained the arrangement of the several va- 

 rieties of fibres, I dissected them out carefully, and measured 

 their lengths. On doing so, it became apparent that the 

 common fibres were equal to each other in length, within the 

 errors of observation ; and also that the proper fibres were 

 equal to each other in length, this length being distinct from 

 the length of the common fibres. This result is caused by 

 the peculiar shape of the heart,* which compels the fibres 

 that enter the interior above the vortex to describe their 

 spiral circumference on a more equatorial region of the heart 

 than the apex ; so that although the return path of these fibres 

 is shorter than that of the superficial fibres that enter the vor- 

 tex, their total lengths remain the same. 



From the preceding statement, it appears that each fibre is 

 independent of the others, and is at full liberty to contract to 

 the utmost extent required by the law of muscular contraction, 

 and thus the law of least action is fulfilled by the common 

 fibres and proper fibres respectively, each fibre belonging to 

 either group having the same length. But, in order that the 

 two groups of fibres, working simultaneously, may produce 

 the maximum of work required by the law of least action, it 

 is necessary that a certain relation should exist between the 



* Or, to speak more correctly, the shape of the heart is the necessary con- 

 sequence of the law of least action, which requires the fibres of the same group 

 to have the same length. 



