MODE OF INSERTION. 295 



extremities and adduction to the foot. This is not dependent 

 upon a difference in length, as was supposed by Borelli, but, 

 according to Beclard, chiefly upon a difference in size, ^nd the 

 relative advantages of insertion upon the bones. 

 Muscles have their tendons attached to the bones, in a man- 

 ner to give them the least mechanical power, but to effect the 

 greatest rapidity of motion ; for, as has been observed by 

 Archdeacon Paley, it is of far greater importance to man, to be 

 able to carry his arm quickly to his head, than to raise several 

 hundred weight more than he is now able to do : the two 

 qualities could not well exist together. All that could be done 

 to increase the power, without impairing the symmetry of the 

 body, or diminishing the celerity of its movements, has been 

 accomplished in endowing the muscles, with an extraordinary 

 force of contraction, at least ten fold as great as the student 

 would at first suppose it. The muscles are nearly all levers of 

 the third order. 



The force with which a muscle contracts, depends upon its 

 volume and the energy of the will, as well as some other circum- 

 stances. But the effect produced by the contraction will 

 depend in a great measure upon the manner in which it is 

 inserted upon the bone on which it acts. 



Thus, all things being the 

 same, the effect of the contrac- 

 tion will be the greater, in propor- 

 tion as the muscle is less obliquely 

 * connected with the bone. Thus 

 if the muscle m, figure 73, the 

 t force of which we suppose equal 



to 10, is fixed perpendicularly to 



the bone Z, the extremity of which a, is movable upon the 

 fulcrum point r, it will have to overcome only the weight of 

 the bone, and will carry it from the position a 6, into the direc- 

 tion of the line a c. But if this muscle acted obliquely upon 

 the bone in the direction of the line n b, it would then tend to 

 carry it in the direction of the line b n, and consequently to 

 force it against the fixed articular surface r. This latter being 



