THE CEREBRUM. 497 



peared, and the head exhibited once again the usual phenomena 

 observed in dying: viz., contraction and then dilatation of the 

 pupils and convulsive movements of the muscles of the face. 

 Localization of Functions in the Cerebrum. By the term 

 localization of functions is meant the assignment of definite phys- 

 iologic functions to definite anatomic areas of the cerebral cortex. 

 From experiments made on the brains of animals, by the observa- 

 tion and association of clinical symptoms with pathologic lesions of 

 the central nerve system, and from observation of the developmental 

 stages of the embryonic brain, it has been established in recent years : 



1. That the general and special sense-organs of the body are as- 



sociated through afferent nerve-tracts with definite though per- 

 haps not sharply delimited areas of the cerebral cortex; and 



2. That certain areas of the cortex are associated through efferent 



nerve-tracts with special groups of skeletal or voluntary muscles. 



Experimental excitation of a cortical area associated with a sense- 

 organ is undoubtedly attended by the production of a sensation at 

 least similar to that produced by peripheral excitation of the sense- 

 organ itself; destruction of the area is followed by an abolition of all 

 the sensations associated with the sense-organ. For these reasons 

 such areas are termed sensor. 



Excitation of a cortical area associated with a group of skeletal 

 muscles is attended by their contraction; destruction of the area is 

 followed by their relaxation or paralysis. For these reasons such areas 

 are termed motor. 



Since the sense-organs are remote from the brain and the impres- 

 sions made upon them by the objective world can be utilized by the 

 mind, only after they have been reproduced in the cortical areas, it 

 may be said that each sense-organ has its special area in the cortex 

 by which it is represented, or, in other words, each sense-organ has 

 a cortical area of representation. 



Since the muscles are remote from the brain and since they 

 contract in response to the discharge of nerve impulses from the 

 cells of the cortical motor areas, it may be said that the activities 

 of the motor areas are represented by the contractions of the muscles ; 

 in other words, that the cortical motor areas have areas of representa- 

 tion in the general skeletal musculature. It is usually stated, how- 

 ever, in the reverse way: viz., that the muscle movements have areas 

 of representation in the cortex. 



The cortex of the cerebrum may therefore be compared to a 

 mosaic made up, partially at least, of sensor and motor areas which 

 respectively represent sense-organs and motor organs, and which 

 bear a definite anatomic and physiologic relation one to the other. 

 Their cooperation is essential to the normal performance of all forms 

 of cerebral activity. 

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