180 



STRUCTURE OF THE VERTEBRATES 



1. L — Lever. 



2. W = Weight, the object to be moved through the arc of 

 a circle by the force exerted on the lever. 



3. F = Fulcrum, the point upon which the lever moves. 



4. P zn Power, the force which moves the lever upon its ful- 

 crum, and thus shifts the position of the weight. It is clear that 

 the position of the fulcrum in relation to the weight ana power 

 will materially influence the speed and force with which the 

 weight is moved. 



M. 



W : F •• ? 



A. 1 St Order 



W. 



M. 



F : P : w 



B. '2^^^ Order 



F : W 

 C. 3'"*' Order 



1 



In Figure I it will be seen that when a weight is held in 

 the hand, and the forearm is flexed, the leverage is like that of 

 the second order (B). AVhen (Diagram II) the back of the hand 

 is pressed against an object as the weight to be moved, the ex- 

 tension of the arm observes the conditions of the first order lever 

 (A). In Diagram III the ball of the foot is the fulcrum, the 

 tibia and fibula support the weight of the body, and the calf 

 muscles act as the power. This is like the third lever (C — 

 F:AV:P), and is powerful although the range of movement is 

 limited and the motion is slow. 



