68 CONSCIOUS NERVOUS OPERATIONS 



The muscle at the back of the humerus applies the power. 

 It is attached by tendons to the scapula and to the hinder 

 side of the humerus, while the tendon into which the lower 

 end of the muscle narrows is inserted into the end of the 

 ulna at the elbow, which is more than an inch above the 

 articulation of the ulna with the humerus. By its contrac- 

 tion the muscle pulls the upper end of the ulna upward, draw- 

 ing down the hand, which is the weight at the lower end of 

 the ulna, and straightening the joint. The fulcrum is at 

 the elbow joint, between the hand and the power at the 

 upper end of the ulna. 



/ \ \ \ \ \ 



in 

 Fig. 45. Diagram of the foot, illustrating levers of the three classes. 



I tapping the toe on the floor. II rising on the toes. 

 Ill lifting a weight with the toes. 



86. Lever of the Second Class. When the body is raised 

 on the toes (Fig. 45, II) the action of a lever of the second 

 class is seen. The weight is that of the whole body sup- 

 ported by the foot at the ankle, while the power operates 

 through the muscles of the calf of the leg at the heel, the 

 toes acting as the fulcrum. 



87. Lever of the Third Class. When the body lying on 

 the ground is raised to a sitting posture, a lever of the 

 third class is used. The head and body are the weight, 

 the fulcrum is at the hip joints, and the power is applied 



