LECT. XVI. MUSCULAR FORCE. 305 



force of the different muscles of the same animal, and which 

 principles are at the present time generally admitted, are as 

 follows : 



1st. Two muscles composed of the same number of 

 fibres, and consequently of equal thickness, can raise a 

 given weight to heights which are proportional to the 

 lengths of the muscles ; or rather, they can raise to a given 

 height weights which are proportional to their lengths. 



2d. If two muscles be of equal length, they can raise to 

 a given height weights proportional to their thickness. In 

 a word, the volume of a muscle determines the weight it 

 can raise; and, on the contrary, the height to which the 

 weight can be raised varies according to the length of the 

 muscle. In more general terms, the mechanical work of a 

 muscle varies according to its length and thickness. It is 

 unnecessary to say that we omit mentioning here an element 

 which is not susceptible of being measured a priori, namely 

 the intensity of the nervous force, which varies with the 

 will. 



It is easy to understand how the extent of motion of the 

 bone depends on the different obliquity with which the 

 muscular fibres are inserted in the tendon, and how it must 

 increase in proportion as the fibres are the more obliquely 

 attached. 



We may also observe that, according to the different 

 obliquity with which the muscle is made to act upon the 

 moveable bone, a greater or less loss of power must ensue. 



Such is the most general arrangement of the motor organs 

 of animals, and we can readily conceive the reason, when 

 we consider that the bodies of both man and animals gene- 

 rally, would have a monstrous form if the muscles acted 

 normally upon the bones. In order to diminish a portion 

 of the loss of the force which the muscles suffer in conse- 

 quence of the obliquity of their insertion on the bones, the 

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