VOLUNTARY MOTION EFFORT. 59 



table; in the unconsciousness of the muscular contraction 

 lies all the merit of this phenomenon, which loses its mar- 

 vellous character as soon as you show the too credulous per- 

 formers that they themselves are the involuntary movers. 



Voluntary movements, as their name indicates, are produced 

 under the influence of the will, but not under its direct or 

 immediate action. The volition of the movements of loco- 

 motion, for example, emanate from a certain part of the 

 brain, from the cerebral lobes; but in order that the move- 

 ment may be executed, the muscles must contract, and this 

 muscular contraction owes its origin to a force which ema- 

 nates from the occipital protuberance, a different part of the 

 brain from that which gives birth to thought. Observations 

 on paralytics prove that the will is insufficient to produce 

 movement. 



In order that movements may be executed in the order 

 and with the unity necessary to the accomplishment of the 

 will, they must be co-ordinate. Several physiologists, and 

 especially Flourens, have regarded the cerebellum as the 

 organ essential to this co-ordination of movement. A lesion 

 of this part of the brain produces a disturbance in locomo- 

 tion similar to that caused by drunkenness ; but pathological 

 observation has demonstrated that there is sometimes absence 

 of co-ordination when the cerebellum is not affected. 



The muscles unite in the voluntary movements, some as 

 motors, and others, antagonistic to these, as the moderators 

 of movement. M. Duchenne (of Boulogne) has shown that 

 in the voluntary movements of the limbs and the trunk these 

 two systems of muscles, impulsive and modifying, are simul- 

 taneously contracted by a double nervous excitation; one to 

 produce the movement and the other to modify it. Without 

 this unity of intention between the antagonistic muscles, the 

 movements would lose their precision and their certainty. 



Effort. When one or several groups of muscles contract 

 themselves strongly in order to perform a function requiring 

 force, or to overcome an obstacle, to draw or push away a 

 body, the name effort has been given to this action of the 

 muscles. There is effort in walking, climbing, running, and 

 a great number of other functions. Whatever muscles take 



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