THE CEREBRUM AND HUMAN DEVELOPMENT 143 



that such cases of epilepsy as those referred to might be 

 due to mechanical sources of irritation acting at the 

 subcenter for that part which was first moved at each 

 seizure. In the course of time operations for the relief 

 of epilepsy were undertaken. Acting on the theory that 

 the brain of man is similar in its large features to that of 

 the ape, the surgeons plotted in advance the presumptive 

 position of the motor areas in general, and of that one in 

 particular which was thought to be subject to abnormal 

 stimulation. In very many cases the spot of cortex which 

 they proceeded to expose was found to be under obvious 

 pressure or otherwise affected by pathologic conditions. 

 A measure of relief from the epileptic symptoms followed 

 such operations, though complete cures were not usual. 



When the surface of the human brain has been laid bare 

 for these operations it has been possible to apply weak 

 electric stimuli to its convolutions, and the movements 

 made by the skeletal muscles of the subject have justified 

 the belief that the organization here is, indeed, closely 

 similar to that in the ape. Microscopic study supports 

 this view. A conspicuous system of projection fibers can 

 be traced from the supposed motor regions inward through 

 the internal white matter of the cerebrum and thence 

 down the brain-stem. In the medulla the great majority 

 of these fibers cross the midline and pass down the cord on 

 the side opposite to that of their origin. They form 

 synapses with motor cells of the cord and so command 

 the muscles. 



The impression prevails that a portion of the cortex just 

 posterior to the motor areas has as a distinctive property 

 the reception of afferent impulses from various parts of the 

 body. It must be remembered that incoming impulses 

 from without the central nervous system never find an 

 uninterrupted path to this level; the original neurons do 

 not pass above the medulla, if, as a matter of fact, they 

 extend so far. It is by synaptic relays that transmission to 

 the cerebral cortex is secured. If we adopt the usual 

 conception of the cortical centers, these areas of reception 



