956 



THE CENTRAL NERVOUS SYSTEM 



of the corresponding area in the opposite hemisphere is now re- 

 moved, a similar paralysis occurs in the other hand, but the hand 

 whose ' motor ' area was first extirpated remains entirely unaffected 

 by the second lesion. On the contrary, the first hand is used more 

 freely and more adroitly than before the second operation, probably 

 because the animal needs to use it more. The second hand recovers 

 eventually, like the first. If when this has taken place the remain- 

 ing part of the arm area from which the hand area was first excised 

 be removed, neither hand is apparently affected, although there is 

 severe paralysis of the shoulder and slighter paralysis of the elbow 

 on the side opposite to the lesion, which is again largely recovered 

 from. The recovery of the hand movement cannot therefore be 

 attributed to the taking on of the function of the corresponding 



Fig. 386. Cerebral Cortex Man (seen from Above). The front of the brain is towards 

 the left. The dotted line shows the position of the fissure of Rolando, as fixed 

 by Thane's rule (p. 963). 



' motor ' area either by the opposite hand area or by the adjacent 

 ' motor ' cortex of the same hemisphere. According to some 

 authorities, the recovery is due to the representation of the upper 

 limb in the post-central gyrus (ascending parietal convolution in 

 man) acting through fibres that descend from this gyrus to the 

 optic thalamus, and thence through the rubro-spinal tract, which 

 runs to the spinal cord (p. 867) . 



Removal of the whole of the ' motor ' cortex of one hemisphere, 

 in such animals as this operation has been performed on, causes 

 paralysis of movement on the opposite side of the body. The 

 paralysis is less marked in the case of bilateral muscles that habitu- 

 ally act together than in the case of those which ordinarily act alone. 

 Thus the muscles of respiration and the muscles of the trunk in 



