ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 701 



cular disturbance nearly entirely disappears, except the regulation 

 of the finer muscular movements. Quite otherwise is the result when 

 you extirpate the motor area in apes. If you remove the whole 

 motor area in a monkey there is a nearly complete paralysis of the 

 muscles of arm and face, and a weakness of the muscles of the pos- 

 terior extremity. There is also difficulty in moving the head to the 

 opposite side. The weakness of the posterior extremity is not so 

 great but that the animal can use it in walking or climbing. 



If in an ape only the motor area of the finger is extirpated, then 

 a permanent weakness in these muscles innervated by this area re- 

 mains, whilst the other muscles are not affected. The result of 

 irritation and extirpation of the cortex in the ape confirms the fact 

 that irritation of a certain motor area always calls out movements 

 of certain muscles, whilst extirpation of the same motor center is 

 followed by a paralysis or weakness of the same muscles. The motor 

 area in the ape is much more important in the muscular movements 

 of the body than the motor area in the dog. The subcortical cen- 

 ters in the dog are not so much under the domination of the activity 

 of the motor centers of the cortex as the subcortical centers in the 

 monkey. The motor centers in man have been established (1) by 

 irritation of the cortex, (2) by anatomical investigations, and (3) by 

 clinical studies and pathological anatomy. The motor area in man 

 has about the same extent as in the ape. 



Flechsig's Association Areas. 



Flechsig, from a study of sections of 56 human brains, has 

 divided the cerebral cortex into 36 areas, of which 12 are myelinated 

 before birth. He was able to determine these areas by the fact that 



the cerebral cortex the fibers take on myelin at different periods, 

 and thus he is enabled to track the fibers. The sensory tracts of the 

 central nervous system take on myelin before birth. The motor 

 tract receives its myelin after birth, but in the spinal nerve roots the 

 anterior are myelinated before the posterior. The first areas to 

 become myelinated are the sense areas smell, touch, muscle-sense, 

 sight, hearing, and taste. The next series of centers to become 

 medullated have at first only fibers within themselves that is, 

 neither projection fibers nor association fibers and Flechsig denom- 

 inates them automatic centers whose function is unknown. The 

 rest of the areas have association bands, and it is most interesting 

 to note that the earlier areas of this group develop as marginal zones 



)und the primary sensory areas and first receive short fibers from 



