460 ACTION OP MUSCLES ON BONES. 



necessary form of the animal body, Muscles are applied at a 

 great mechanical disadvantage as regards the exercise of their 

 power ; that is, a much larger force is employed than would 

 suffice, if differently applied, to overcome the resistance. But 

 we generally find that, in this as in other forms of lever action, 

 what is lost in power is gained in time ; and thus a very slight 

 change in the length of a muscle is sufficient to produce a 

 considerable movement. 



610. The first source of disadvantage results from the 

 direction in which the muscle is attached to the bone. This 

 is rarely at right angles to it ; and consequently a considerable 

 part of the power is lost (see MEGHAN. PHILOS., 299). Thus 

 if the muscle m (fig. 213), whose force we shall suppose equal 



to 10, be fixed at right angles 

 to the bone /, whose extremity 

 a is movable upon the point of 

 support r, its force of contrac- 

 tion will be most advantageously 

 applied to overcome the resist- 

 ance, and will draw the bone 

 from the position a b into the 

 direction a c, making it traverse 

 a space which we shall also 

 represent by 10. But if this muscle act obliquely on the 

 bone, in the direction of the line n b for example, it will 

 be quite otherwise ; for it will then tend to draw the bone 

 in the direction b n, and will consequently make it approach 

 the articular surface r. But as this bears upon an immovable 

 socket, and as the bone can move in no other way than by 

 turning upon the point r as upon a pivot, the contraction of 

 the muscle to the same amount as before will carry the bone 

 no further than into the direction a d ; three-quarters of the 

 force employed will thus be lost, and the resulting effect will 

 be no more than one-fourth of that which the same power 

 applied perpendicularly to the bone would have produced. 



611. We usually find that the muscles are inserted so 

 obliquely, that their power is applied at a great disadvantage ; 

 but this disadvantage is rendered much less than it would 

 have otherwise been, by a very simple contrivance, that very 

 enlargement of the bones at the joints which is necessary to 

 give them the required extent of surface for working over 



