268 THE NERVOUS SYSTEM 



Cerebral Localization. There are certain cortical areas 

 which have certain fixed functions. There are certainly such 

 areas for motion and for the reception of impressions conveyed by 

 the nerves of special sense; areas for the reception of impressions 

 conveyed by the nerves of general sensation have not been defin- 

 itely determined. 



Motor Centers. Electrical stimulation of the convex surface 

 of the cerebrum shows that the anterior part is motor and the 

 posterior part non-motor; that stimulation of the motor por- 

 tion produces muscular contractions on the opposite side of the 

 body, that stimulation in the same spot is always followed by 

 the same contractions; and that when the current is quite weak 

 the contractions are limited to distinct muscles or sets of muscles. 

 It may be further said that while experiments establishing these 

 facts have been largely limited to inferior animals, the deductions 

 have been made applicable to man by pathological observations 

 and by the fact that in different animals stimulation of anatom- 

 ically corresponding parts is followed by corresponding results. 

 Destruction of motor areas is followed by descending secondary 

 degeneration of fibers through the corona radiata, internal cap- 

 sule, crura cerebri (crusta), anterior pyramids of the medulla and 

 the pyramidal tracts of the cord; the resulting paralysis is on the 

 side opposite the lesion. 



The motor cortical zone, so far as can now be said, corresponds 

 to the ascending frontal and parietal convolutions on either side 

 of the fissure of Rolando, to the paracentral lobule, and possibly 

 to a small area in front of the ascending frontal convolution. 

 From above downward, on either side of the Rolandic fissure 

 are areas presiding over the movements of the leg, arm and 

 face. 



More specific information as regards areas controlling various 

 movements may be obtained by reference to Fig 86. 



Various kinds of monoplegia (crossed) are caused by lesions, 

 as hemorrhage, in localized parts of the motor area; there may 



