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HUMAN PHYSIOLOGY 



of this area on one side cause a loss of the so-called voluntary 

 action of groups of muscles on the opposite side of the body. 

 The cerebral arc is stimulated and acts along certain lines 

 possibly with the accompaniment of consciousness in a sen- 

 sation of decision as to the line of action to be taken and a 

 desire to accomplish it but this so-called volition is not 

 accompanied by the appropriate muscular action. From 

 the frequent involvement of the so-called volition in these 

 actions, and from the fact that these metaphysical changes 



Fio. 99. Left Hemisphere of Brain of Chimpanzee to show the results of stimu- 

 lating different parts. The Sulcus Centralis is the fissure of Rolando. (Front 

 GRCNBAUM AND SHERRINGTON.) 



figure more largely in our consciousness than the physical 

 changes which are their basis, we are accustomed to assume 

 that the movements produced are the result of volition, and 

 to speak of them as voluntary movements, and of the brain 

 mechanism producing them as voluntary centres. There is 

 no harm in doing so if we remember that these centres can and 

 do act without the involvement of consciousness, and, there- 

 fore, without volition ; but that their action generally implies 

 the previous action of parts of the receiving and associating 

 mechanism of the cerebrum. 



But certain lesions may directly stimulate these centres, 



