378 THE POPULAR SCIENCE MONTHLY. 



the brain ; and since no muscle normally contracts except under 

 the stimulus of a nervous impulse transmitted through a nerve- 

 fiber from the central nervous system, my first thesis will be at 

 once admitted, viz., that exercise of muscles necessarily involves 

 exercise of their associated regions in the central nervous system, 

 and that voluntary movements at least require the activity of cer- 

 tain areas of the brain. 



It is admitted that the evolution of mind in the animal series 

 and that of the bodily organs have kept pace with each other. 

 The hemispheres of the brain increase in size and in complexity 

 in the ascending zoological scale, the animal becoming mentalized 

 in a direct ratio to the development of this part of the brain, 

 which in man forms by far its largest subdivision. The doctrine, 

 first definitely formulated by Fritsch and Hitzig, that the cortex 

 of the brain contains special centers which govern definite groups 

 of muscles,* is most significant in connection with this subject. 

 They and their followers divide the brain cortex into two princi- 

 pal regions — one of sensory areas, which lie in the hinder part of 

 the brain, and another of motor areas, which lie anteriorly ; i. e., 

 into a region engaged in receiving from the surface organs (the 

 skin, the eye, etc.) impressions which excite the various sensa- 

 tions, and a region concerned in exciting and co-ordinating the 

 movements of the body. The motor centers thus far definitely 

 located are those which control the muscles of the face, arm, leg, 

 and trunk. They lie on each side of one of the fissures of the 

 brain, f in the order named from below upward — an arrangement 

 which led Dr. Lauder-Brunton to suggest that it had occurred 

 in accordance with the progressive evolution of the faculties, 

 premising that the uppermost in position were the latest to be 

 acquired and the highest functionally. Thus animals low in the 

 scale seize their food with the mouth; the center for the face- 

 muscles was therefore earliest in order of development, as it is 

 lowest in situation. Animals of a somewhat higher grade grasp 

 their food with the anterior limbs— the next higher centers being 

 those devoted to the arm-movements. Animals still further ad- 

 vanced in development have the power of running after their 

 prey, using the posterior to assist the anterior limbs in accordance 

 with the higher level of the centers concerned. Later still, the 

 trunk muscles come to the assistance of the arms and legs in 

 the all-important work of securing food, the first necessity. Co- 

 incident with these observations is the fact that the higher the 

 center the more it requires education in the human being. The 

 new-born infant has control of the muscles of the mouth to 



* Known as the doctrine of localization. 



f The fissure of Rolando, anterior to the fissure of Sylvius which separates the motor 

 from the sensory areas. 



