MUSCLES AND MOTION 89 



other the Weight, the arrangement is called a lever of the 

 third class (see Fig. 43, C). 



LVIL LEVERS OF THE BODY (OPTIONAL). 



Directions. A. Locate on the upper arm the biceps 

 muscle, or flexor of the arm. Where is it attached to the 

 forearm and how far (perpendicular distance) from the 

 elbow? Measure the perpendicular distance from the elbow 

 to the center of the palm. If now we put a weight of 

 ten pounds in the palm and bend the arm, what class of 

 levers is illustrated? How much force is required on the 

 part of the muscle to raise ten pounds' weight? By se- 

 lecting different weights to lift, determine the maximum 

 strength of the biceps muscle. What muscle is used in 

 striking an outward blow with the fist? Where is it located 

 and inserted? Note that the flexors and extensors in other 

 parts of the body are usually arranged in pairs. 



B. Examine the relation of the muscle, weight, and pivot 

 in the following cases, and tell which class of lever each 

 illustrates : Jaw action in chewing, flexing of the fingers, 

 movement of the legs in kicking, bending the body, move- 

 ment of the foot about the ankle (see Fig. 43). 



NOTE. The instructor can suggest other problems of the above 

 nature to make clear the laws of lever action. 



