222 MENTAL AND PHYSICAL EXERCISE. 



So far as mechanical advantage is concerned the last 

 is by far the less effective, and it is the application of 

 this principle by which the levers are moved by the mus- 

 cles. We shall see however, that it is not mechanical 

 power alone which is created in the construction of the 

 limbs, and that all the circumstances considered, this is 

 the only kind of lever which could be employed consist- 

 ently with the perfection of our organs of motion. 



Muscular action of the Arm and Hand. The motion 

 of the fore arm may be taken as an example of the 

 effect of muscular contraction, and the manner in which 

 it is produced in the animal system. When we raise a 

 weight by bending the elbow joint, this is effected by 

 muscles situated below the shoulder with the tendons 

 inserted into the upper sides of the bones of the fore arm 

 just below the joint. 



Let a b, Fig. 122, represent the bones of the fore arm, 

 b d, the bone of the arm, d the muscle, e the tendon, c 



Fig. 122. 



the insertion of the tendon into the radius, and b the 

 elbow joint. It is plain that the contraction of the mus- 

 cle, makes c approach towards d, which, as d is a fixed 

 point is effected by bending the joint 5, raising up the 

 point c, and thus giving great velocity of motion to , 

 and the weight attached to it. 



" The consideration of the manner in which the mus- 

 cle acts in this case, proves that the mechanism of the 

 animal body is calculated to produce a great loss of 

 absolute power. It is an established position in mechan- 

 ics, that in the action of levers, the power is to the 

 weight as the distance between the weight and the ful- 



Whatkind is applicable to the bones 7 Explain Fig. 122, and show 

 why much mechanical force is lost in that arrangement '.' Why is mus- 

 cular power thus sacrificed 1 



