CHAPTER XXVIII 

 MOVEMENTS OF THE LIMBS 



" If the mountain will not come to Mohammed, 

 Mohammed must go to the mountain." 



IN order to get food, prepare food, and preserve its life and that 

 of its race, the higher animal makes use of a series of levers to 

 move its body in whole or in part. These levers are generally, 

 but not always, made of bone, and generally but not always they 

 work against a bony fulcrum. 



In general, a lever is a rigid bar either straight or curved which 

 is capable of a rotatory motion round a fixed point the fulcrum. 

 It is usual to divide levers into three classes depending on the 

 relative positions of power, fulcrum and load. 



Class I. The fulcrum lies between the power and the load. 

 In this class of lever, if the power arm is equal to the load arm, we 

 have a balance. The application of one kg. of power will lift one 

 kg. of load. If the power arm is lengthened by shifting the 

 fulcrum nearer to the load, then power will be increased propor- 

 tionally as speed is decreased. For example, dealing with a 

 straight lever and putting P=point of application of power, 

 jF=fulcrum and L=point of application of load, then PF 

 represents the length of the power arm, and LF=length of 

 the load arm of the lever. If PF=10 times LF, then 1 kg. 

 at P would balance 10 kg. at L, i.e. the load of 10 kg. would be 

 lifted by the exertion of a little over 1 kg. weight. This is the 

 crowbar lever and is very little employed in the body. The 

 most notable example of it is the forwards and downwards move- 

 ment of the head when one is overtaken by unconsciousness, e.g. 

 sleep. The fulcrum on which the head moves is the atlas, and 

 the weight of the prefulcral part of the head (long power-arm) 

 outbalances the postfulcral portion (short load-arm). 



Generally, speed is the desideratum. The fulcrum is placed 



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