254 MOTION AND COORDINATION 



forearm), it is easily shown that the gain in motion 

 causes a corresponding loss in muscular power. (See 

 Practical Work.) If, for example, the balance is attached 

 two inches from the fulcrum and the weight twelve inches, 

 the pull on the balance is found to be six times greater 

 than the weight that is being lifted. If other positions are 

 tried, it is found that the power exerted in each case is as 

 many times greater than the weight as the weight-arm is 

 times longer than the power-arm. 



Applying this principle to the levers of the body, it 

 is seen that the gain in motion is at the expense of 

 muscular force, or, as we say, muscular force is exchanged 

 for motion. This exchange is greatly to the advantage 

 of the body ; for while the ability to lift heavy weights 

 is important, the ability to move portions of the body 

 rapidly and through long distances is much more to be 

 desired. 



Important Muscles. There are about five hundred sep- 

 arate muscles in the body. These vary in size, shape, and 

 plan of attachment, to suit their special work. Some of 

 those that' are prominent enough to be felt at the surface 

 are as follows : 



Of the head : The temporal, in the temple, and the mas- 

 seter, in the cheek. These muscles are attached to the 

 lower jaw and are the chief muscles of mastication. 



Of the neck: The sterno-mastoids, which pass between 

 the mastoid processes, back of the ears, and the upper 

 end of the sternum. They assist in turning the head and 

 may be felt at the sides of the neck (Fig. 119). 



Of the upper arm: The biceps on the front side, the 

 triceps behind, and the deltoid at the upper part of the 

 arm beyond the projection of the shoulder. 



Of the forearm : The flexors of the fingers, on the front 



