THE CEREBRUM 593 



her of such sense areas may be predicated: e.g., areas of cutaneous and muscle 

 sensibility, of gustatory, olfactory, auditory, and visual sensibility. 



The Motor Areas. The motor areas which should theoretically be 

 present in the cortex are those which in consequence of the discharge of nerve 

 impulses excite contraction of special groups of muscles and which, from 

 their coordinate and purposive character, are conventionally termed voli- 

 tional. Five such general motor areas may be predicated: e.g., one for the 

 muscles of the head and eyes, one for the muscles of the face and associated 

 organs, and others for the muscles of the arm, leg, and trunk. They are 

 usually designated as head and eye, face, arm, leg, and trunk motor areas. 



The existence and anatomic location of the sensor and motor areas in 

 the cortex of animals have been determined by the employment of two 

 methods of experimentation: viz., stimulation and destruction or extir- 

 pation; the first by means of the rapidly repeated induced electric cur- 

 rents, the second by the electric cautery and the knife. 



If the stimulation of a given area is attended by phenomena which indi- 

 cate that the animal is experiencing sensation, and its destruction by a loss 

 of this capability or the loss of a special sense, it is assumed that the area is 

 sensor in function is an area of special sense. If the stimulation or excitation 

 of any given area is followed by contraction, and its destruction by paralysis 

 of muscles, it is assumed that the area is motor in function is an area of 

 motion. 



The animals generally employed for experiments of this character are 

 dogs and monkeys, though other animals have frequently been employed by 

 different investigators. Of all animals, the monkey is the most frequently 

 selected, as the configuration of the brain in its general outlines more closely 

 resembles that of man than does the brain of any other animal. The results 

 therefore which are obtained, there is every reason to believe, are the results, 

 in their general outlines, that would follow stimulation of the human brain 

 if this were possible under the same conditions. Indeed, the clinical symp- 

 toms which arise during the development of pathologic processes, and the 

 phenomena which occur during surgical procedures for the removal of 

 growths and pathologic cortical areas, justify the conclusion that the sen- 

 sor and motor areas which have been located in the monkey brain, may be 

 transferred to the human brain without introducing any very serious 

 errors. 



The Sensor and Motor Areas of the Monkey Brain. From experi- 

 ments made on the brains of monkeys, Ferrier, Schafer, Horsley, and many 

 others have mapped out, though not with a high degree of definiteness and 

 certainty, a number of areas, stimulation of which gives rise to sensation, 

 while their destruction is followed by a loss of sensation on the opposite 

 side of the body. Collectively these areas are known as sensor areas and 

 are as follows: 



1. A tactile area or an area for tactile sensibility. 



2. An olfactory and a gustatory area or areas for olfactory and gustatory 



sensibility. 



3. An auditory area or an area for auditory sensibility. 



4. A visual area or an area for visual sensibility. 



These same investigators have mapped out a number of other areas, stimu- 

 lation of which gives rise to contraction of muscles on the opposite side of 

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