1 88 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 phen- 

 omena 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 localizing 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 centers most 

 definitely mapped out and that are of paramount importance. 



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. 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 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. 



For diagnostic purposes the motor areas for the face and limbs have been 

 subdivided as follows: 



i. The face area may be divided into an upper part, comprising about one 

 third, and a lower part, comprising the remaining two thirds. In the 

 upper part are centers governing the movements of the muscles of the 

 opposite angle of the mouth and of the lower face. The anterior portion 

 of the lower two thirds controls the movements of the vocal cords, and 

 may be regarded as a laryngeal center; the posterior portion governs the 

 opening and shutting of the mouth and the protrusion and retraction of 

 the tongue. 



