STRUCTURE AND FUNCTIONS OF THE CEREBRUM 149 



with the cell-bodies of motor neurons indicates that they form 

 the paths by which the cerebrum exercises control over bodily 

 movements. The anatomical evidence for that view has been 

 corroborated and strengthened by physiological evidence. The 

 German physiologists, Fritsch and Hitzig, showed that in dogs 

 electrical excitation of those areas of the brain from which spring 

 the pyramidal tracts is followed by movements of the muscles of 

 the Body. They showed also that these are the only areas from 

 which such movements can be elicited. 



Upon the basis of all this evidence we are justified in looking 

 upon the regions immediately in front of the Rolandic fissures 

 as motor areas. These areas have been much studied physiologi- 

 cally in recent years. The brains of the higher apes have been 

 preferred in these studies to those of lower animals because of 

 their greater similarity to the human brain. 



There have been a few observations upon the brains of human 

 beings in cases where the surgical treatment of certain diseases 

 has involved removal of portions of the skull overlying the Ro- 

 landic areas. 



These recent studies have shown that there is a considerable 

 localization within the motor areas themselves; stimulation of one 

 point causes movements of the hand, of another the foot, of still 

 another the head. They have shown incidentally, also, that the 

 cerebral cortex is not painfully sensitive to direct stimulation. 

 The men whose brains were excited electrically in the observa- 

 tions cited above were conscious throughout the procedure and 

 reported no sensations of pain or discomfort at any stage. 



Cortical Reflex Paths. The various sensory areas with their 

 afferent nerve-paths afford means whereby impulses may enter 

 the cerebrum from the different receptors; the motor areas, one 

 in each hemisphere, with their efferent paths, provide for the 

 passage of impulses from the cerebrum to the motor organs of the 

 Body; the abundant equipment of association fibers within the 

 cerebrum makes possible the passage of impulses across from 

 sensory areas to motor areas. We can picture, then, reflex arcs 

 involving the cerebrum. Such arcs are necessarily complex, in- 

 volving many more neurons than do the simple spinal cord reflex 

 arcs already described. In a previous paragraph (p. 136) we saw 

 that the simplest reflex arc through the cord involves at least 



