THE CEREBRUM. 547 



itself; and secondarily those which receive and translate into conscious sensa- 

 tions the nerve impulses developed in the special sense-organs by the impact of 

 the external or objective world. In the former areas, are received the nerve 

 impulses that come from the mucous membranes, muscles, joints, viscera, etc., 

 and give rise to muscle, and visceral sensations. In the latter areas are 

 received the nerve impulses that come from the sense-organs and give rise 

 to cutaneous, e.g., tactile, thermal, painful, gustatory, olfactory, auditory, 

 and visual sensations. A number 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 these areas in the cortex of 

 animals have been determined by the employment of two methods of ex- 

 perimentation: viz., stimulation and destruction or extirpation; the first 

 by means of the rapidly repeated induced electric currents, the second by 

 the electric cautery and the knife. 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 a center of 

 motion. If the stimulation of a given area is attended by phenomena 

 which indicate 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. The animals gener- 

 ally 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 configura- 

 tion 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 symptoms 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 chart of the sensor 

 and motor areas of the monkey brain may be transferred to the human brain 

 without introducing any serious errors. 



The Sensor Areas of the Monkey Brain. From experiments 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, 

 the sensor areas, stimulation of which gives rise to sensation, destruction to 

 loss of sensation. A diagrammatic representation of these areas is shown 

 in Fig. 250 and Fig. 251. 



The tactile area or area of tactile perception has not been accurately or 



