210 HUMAN PHYSIOLOGY. 



CEREBRAL LOCALIZATION OF FUNCTIONS. 



From experiments made upon animals, and from the results of 

 clinical and post-mortem observations upon men, it has been shown 

 that the phenomena of organic and psychic life are presided over 

 by anatomically localized centers in the brain. A knowledge of the 

 position of these centers becomes of the highest importance in local- 

 izing the seat of lesions, thrombi, hemorrhages, new growths, etc., 

 which show themselves in paralyses, epilepsies, etc. It has not 

 been possible to thus localize all functions, and to many parts of 

 the brain no special use can be assigned. The following are the cen- 

 ters most definitely mapped out and that are of paramount im- 

 portance. 



Motor Centers. These are in the cortical gray matter, and are 

 arranged along either side of the fissure of Rolando. This area is 

 known as the motor area or motor zone, stimulation of which is 

 followed by convulsive movements of the muscles of the opposite 

 side of the body, while destruction of the gray matter of this area 

 is followed by permanent paralysis of the muscles of the opposite 

 side. From experiments made upon monkeys, Ferrier has mapped 

 out a number of motor centers which he has transformed to corres- 

 ponding localities on the human brain. (See Fig. 26.) The de- 

 scriptive text of the illustration renders his results intelligible. 

 Pathologic studies have largely confirmed his deductions. In a gen- 

 eral way it may be said that the upper third of the ascending frontal 

 and parietal convolutions about this fissure preside over the move- 

 ments of the leg of the opposite side of the body ; the middle third 

 controls the movements of the arm ; the upper part of the inferior 

 third is the facial area. The lowest part of the inferior third gov- 

 erns the motility of the lips and tongue, and this space, with the 

 posterior extremity of the third frontal convolution, constitutes 

 the speech center. 



The experiments of Horsley and Schafer have enabled them to 

 furnish a new diagrammatic representation of the motor area and 

 more accurately to define the special areas upon the lateral and 

 mesial aspects of the brain of the monkey. The boundaries of the 

 general and special areas, as determined by these observers, will be 

 readily understood by an examination of Figures 27 and 28. 



