MOTOR AREAS OF THE CEREBRUM 



885 



sign of affection or memory of its master, it does not recognize food as 

 good to eat by its mere appearance, nor does it give signs of dreaming as 

 normal dogs do. The mechanism by which the retention and association 

 of the effects of past experience modifies behavior and produces acts of 

 an apparently spontaneous and volitional nature evidently resides in 

 the complicated meshwork of neurons which compose or connect the 

 various parts of the cerebral cortex. 



The Motor Areas of the Cerebral Cortex 



Just as we saw in the last chapter that there were certain junction 

 points, or sensory areas, by which afferent impulses are led into the 



Anus & Vagina 



Toes/?' 



Ankle ; 



Knee 



,Sulcus centralis 



-Abdomen 



Shoulder- 



Fingers 

 sthum 



YES 



Sulcus centrolis 



Fig. 217. Outer aspect of the brain of the chimpanzee, showing the position of the motor centers. 

 Electric stimulation at the parts indicated causes coordinate movements of the corresponding mus- 

 cle groups. (After Sherrington.) 



cerebral cortex so there are certain foci from which efferent impulses 

 leave the cortex to initiate movement in the skeletal muscles. ' These 

 are the motor areas of the cortex. Their situation and the groups of 

 muscles related to each part of the motor area have been made out by 

 two methods. In animals, and, under exceptional conditions, in man, the 

 cortex may be excited locally, preferably by some method of unipolar 

 electrical stimulation, and the groups of muscles brought into action 

 may then be noted. By this method the most precise data has been 

 obtained, especially in experiments upon the higher apes, the topography 



