460 ACTION OF 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 Mzcnan. Puinos., § 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 
..r support 7, its force of contrac- 
tion will be most advantageously 
applied to overcome the resist- 
ro : ance, and will draw the bone 
geiiay ng 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 » 6 for example, it will 
be quite otherwise ; for it will then tend to draw the bone 
in the direction 6 n, and will consequently make it approach 
the articular surface 7, But as this bears upon an immovable 
socket, and as the bone can move in no other way than by 
turning upon the point 7 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 ad; 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 ve 
enlargement of the bones at the joints which is necessary 
give them the required extent of surface for working over 
Fig. 213. 
