THE BRAIN OF MODERN MAN 803 



and upper extremity has so progressed over and above the adajjtix e ehangcs 

 manifest in thele<i;and loot tliat tliis dillerentiation de facto e\])lains the dis- 

 parit\ in size l)et\veen tlie two sensory cohinins. If the striiet ural chllertMitia- 

 tion aloni' weie the (k'tt'rnunin>j; ni()ti\'e in tht- expansion w hieh oeeurs ni tlie 

 eohinm of Burdaeh, it is jjrohable that no siieh chsparit\' wmild he exident. 

 The greater size of the fascicuhis cuneatus must Ije attributed more to the 

 funetional expansion arising in eonnt'etion with the wide inerease in range of 

 mo\<-'ment now possible in the hand. 1 lie total number ol postures and 

 museular eoml)inatioiis of myotensional states ior liiieness ol moxement 111 

 the human upper extremit\ has shown a pronouneed inerease as compared 

 with any of the other primates. This large number of joint and muscle 

 combinations incident to complex manual manipulation 111 man has called 

 forth a corresponding increase in the sensory inllux. Although in the great 

 anthropoids there has been a marked tendency to establish a similar diOer- 

 ence in the size of the columns of Goll and Burdaeh, thus signifying that the 

 forelimb was becoming progressively more emphatic in its influence as a 

 sensory organ, the linal stage is reached in man. The contrast is most con- 

 vincing on comparing the human conditions with such low forms as the 

 tarsius or marmoset. The nervous system rellects 111 these particulars the 

 modifications occurring in the upper extremity and Iiand. 



Another feature descrxing emphasis is the fact that the entire sensory 

 field IS considerably larger than in the lower jarimates. The total sensory 

 inllux from the i-xtremities, both upper and lower, appears to be of larger 

 volume in man than m aj^cs. 



Lateral to the column of Burdaeh is the substantia gelatinosa trigemini 

 (NR) on whose outer margin is the descending trigeminal tract (Trd). 

 The reticular formation ( Ref) is well delined and lies in a j)()sition dorsal 

 to the \entral gra\' column. In the circumferential and intermediate zones in 

 the medullary substance are the two ascending spinocerebellar tracts (Fie, 



