434 



ANIMAL MECHANICS. 



aimed at in the construction of the gun could have been 

 completely fulfilled in practice, all the eight rings would have 

 been ruptured simultaneously when the bursting charge of 

 the gun was reached. 



Having shown by the preceding example the conditions 

 required by the principle of" Least Action" when applied to 

 the heart, I shall now describe the actual arrangement of the 

 fibres of the heart, and demonstrate that the law of least 

 action is completely fulfilled by them. The heart has been 

 compared by Borelli and Winslow to two muscles enclosed 

 in a third, and the fibres composing these three muscles may 

 be classified as follows : — 



i°. Common fibres passing round both ventricles. 



2°. Proper fibres passing round the left ventricle. 



3°. Proper fibres passing round the right ventricle. 



I shall commence by describing the course of the common 

 fibres. The muscular fibres of the auricles and ventricles, 



Fig. ioo. 



forming quite distinct systems, both take origin from the 



