THE CENTRAL NERVOUS SYSTEM 



849 



habitually act together than in the case of those which ordinarily 

 act alone. Thus the muscles of respiration and the muscles 

 of the trunk in general are, although perhaps weakened, never 

 completely paralyzed. 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 



353. BRAIN OF MACAQUE MONKEY (BEEVOR AND HORSLEY). 

 The upper figure shows the lateral aspect of the left hemisphere, and the lower 

 figure its upper (or dorsal) surface. The ' motor ' and sensory areas are indicated. 

 It is questionable whether the * motor ' region is as extensive as represented. 

 Some observers do not admit that it extends behind the central sulcus in these 

 lower monkeys any more than in the higher apes. 



of the ' motor ' cortex, -or injury to the pyramidal tracts in the 

 internal capsule or cms, some degenerated fibres (homolateral 

 fibres) are found in the crossed pyramidal tract on the side of 

 the lesion (p. 778). 



In the dog after a time the -.paralysis may more or less com- 

 pletely disappear. In the monkey restoration is less complete. 



54 



