CEREBRAL LOCALIZATION OF FUNCTION. 143 



ducing reflex or instinctive movements. The pigeon can be temporarily 

 aroused by pinching the feet, loud noises, light placed before the eyes, etc., 

 but soon relapses into a state of quietude, being unable to remember im- 

 pressions and connect them with any train of ideas ; the faculties of 

 memory, reason and judgment being completely abolished. 



CEREBRAL LOCALIZATION OF FUNCTION. 



From experiments made upon animals, and the results of clinical and post- 

 mortem observations upon men, it has been shown that the phenomena of 

 organic and psychical life are presided over by anatomically localized centres 

 in the brain. A knowledge of the position of these centres becomes of the 

 highest importance in localizing the seat of lesions, thrombi, hemorrhages, 

 new growths, etc., which show themselves in paralysis, 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 centres 

 most definitely mapped out and that are of paramount importance : 



Motor Centres. 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 destruc- 

 tion 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 centres which he has transferred 

 to corresponding localities on the human brain (see Fig. 16). The descrip- 

 tive test of the figure renders his results intelligible. Pathological studies 

 have largely confirmed his deductions. In a general way it may be said 

 that the upper third of the ascending frontal and parietal convolutions 

 about this fissure preside over the movements 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 governs the motility of the lips and tongue, and this space, 

 with the posterior extremity of the third frontal convolution, constitutes the 

 speech centre. 



The experiments of Horsley and Schafer have enabled them to furnish 

 a new diagrammatic representation of the motor area and to more accurately 

 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 deter- 



