FUNCTIONS OF THE BRAIN 



923 



' 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. 839). 



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 



Fig. 371. 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. 929). 



general are, although perhaps weakened, never completely para- 

 lyzed. This is an indication that each member of such functional 

 pairs of muscles is innervated from both hemispheres; and this 

 physiological deduction is supported by the anatomical fact already 

 referred to, that after removal of the ' motor ' cortex, or injury to 

 the pyramidal tracts in the internal capsule or crus, some degener- 

 ated fibres (homolateial fibres) are found in the crossed pyramidal 

 tract on the side of the lesion (p. 847). 



In the dog after a time the paralysis may more or less completely 

 disappear. In the monkey restoration is less complete. 



Some interesting observations have been made on a monkey, 

 which was carefully watched for eleven years after the removal by 

 two operations of the cortex of the greater portion of the frontal 



