CORTICAL LOCALIZATION OF FUNCTION 



961 



for mental integrity, which is about 1000 grams (35 ounces avoirdupois) in the 

 male and 900 grams (31.7 ounces avoirdupois) in the female. Certain idiotic- 

 individuals possess brains of normal size or even abnormally large brains, but 

 structural defects underlie these forms of idiocy. 



The whale, porpoise, dolphin, and elephant possess larger brains than man, 

 but relative to the size and weight of the body the human brain is proportionately 

 larger. 



CORTICAL LOCALIZATION OF FUNCTION. 



Patient researches conducted along clinicopathological, experimental, physiological, and de- 

 velopmental lines have furnished us with a topographic map of the somesthetic and sense 

 areas, and, inferentially, of the association areas of the cerebral cortex. The somesthetic and 

 sense areas constitute less than one-third of the cortical area, while the remainder is presumed 

 to be devoted to the elaboration of the higher mental activities manifested by abstract thought, 

 ideation, reasoning, and language. The acquisition of these specifically human mental attri- 

 butes has been the chief factor in bringing about the superior structure of the human brain, and 

 those cortical regions which were subjected to increased associations rose in functional dignity 

 and increased in size. With over nine billion functional nerve cells in the human cerebral 

 cortex devoted to the mental processes, and less than one-third of these concerned with emissary 

 and receptive functions, the intricacy and capacity of the human brain for the manifold registra- 

 tion of sensations and the numerous transformations that characterize man's mental process 

 far exceed that of any other animal. 



M USCULAR SE/Vs e 



FIG. 712. Mesal view of left cerebral hemisphere, showing localization of functions. The schema of the 

 fissures and gyres is the same as in Fig. 636. 



The delineation of areas called motor, visual, auditory, etc., is not to be deemed as mathe- 

 matically accurate or sharply defined as the boundaries of a State, county, or township. The 

 areas rather shade off in a diffuse manner, and the arbitrary demarcations employed in the 

 appended figures merely show the maximum concentration of those cortical parts which most 

 distinctly appertain to the function alleged for them. 



The principal areas that are known to be functionally differentiated are the following: 

 1. Motor Area. The motor area comprises the precentral gyre and parts of the frontal gyres 

 adjacent thereto, together with the paracentral gyre and the adjacent portion of the superfrontal 

 gyre on its mesal face. Stimulation of various parts of this area causes movement, while their 

 destruction impairs or abolishes voluntary movements. Within this motor area may be defined 

 districts which are cortical projections of the muscular systems of the body. Thus, movements 

 of the lower limb seem to be controlled by the dorsal part of the precentral and the paracentral 

 gyre; the trunk musculature by the area lying frontad both on the mesal aspect and in the dorsal 



