CHAPTER XI 



THE CEREBRUM AND HUMAN DEVELOPMENT 



THE motor areas of the cerebral cortex were fir>t 

 demonstrated by experiment^ upon the doi. and later 

 <lio\vn to exist in the brain of the ape. In the cerebrum 

 of man they are known to occupy a similar portion and 

 to have the same properties. This i> to >ay. that when 

 points within them are electrically excited, movement 

 result, and chiefly on the part of muscles on the opposite 

 side of the body. The subdivisions of the uvneral motor 

 area are permanent in the sense that the same ^roup of 

 mu.M'le- ;il\vays responds when a selected -pot i> -tinui- 

 lated. The areas are better developed in man than in 

 the ape, and better in the ape tl an in the dor or the cat. 

 This is in harmony with the fact that muscular move- 

 ments in the lower animals are largely piverncd by means 

 of reflex arcs that do not a>cend into the cerebrum. It 

 follows naturally that injury to the motor regions in man 

 re-nits in irreparable interference with muscular move- 

 ments, though we have seen that in the doii' the entire 

 cerebrum may be destroyed and the power of locomotion 

 remain. 



It may >eeni strange that the existence of motor area> 

 should have been proved for the human brain. The facts 

 are a- follou-: In certain types of epilepsy it was noted 

 IOHL: au'o that each attack is ushered in by an invariable 

 initial movement. The clo^inir of one fist or the d ra \\in.ti' 

 of the lips toward one >ide may irive a reliable warning 

 of the approaching convulsion, \\heii it became known 

 lhat definite motor areas occur in the brain of 1 he ape, 

 the -uru'eon- conjectured that homologous areas mi^ht 

 be a<-umeil to have their place in the brain of man, and 



