468 



M O T I O N. 



mouth by depressing the lower jaw, is an example of the same 

 kind, the tension of the muscles which close the jaw repre- 

 senting the weight (Fig. 164). 



In a lever of the third kind the arrangement is F.P.W., 

 and the act of raising a pole, as in Fig. 165, is an example. 

 In the human body there are numerous examples of the em- 



ployment of this kind of leverage. The act of bending the 

 forearm may be mentioned as an instance (Fig. 165). 



In the human body, levers are most frequently used at a 

 disadvantage as regards power, the latter being sacrificed for 

 the sake of a greater range of motion. Thus in the diagrams 

 of the first and third kinds it is evident that the power is so 

 close to the fulcrum, that great force must be exercised in order 



