THE BRAIN OF PREHISTORIC MAN 879 



cluiracUT. riu' base of this lobe, as seen in the occipito-panetal region, indi- 

 cates an increase in all diameters. I^rofessor McGregor's supplementary 

 reconstruction likewise shows decisive expansion in this lobe. I he most 

 jironounct'd cortical increnu'iit appears to ha\e iinoKed the superior and 

 middle temporal fi.\ res in the area assigned to auditory function. Although 

 it seems unwise to be categorical in this matter, all of the axailable evidence 

 warrants the assumption that the sense of hearing had lollowed the t'xample 

 of sight and bod\- sense in seeking broader lields lor its actixities in the neo- 

 palliLim. Such auditory expansion is indispensable to vocal speecii, since 

 symbolic sounds ari' usually acquired through hearing belore the\ may be 

 reproduced b\ articulation. 



All four of the great neopallial lobes of the pithecanthropus hemispht'rcs 

 give evidence ot increased si/e and hence augmented hinctioiial capacity 

 when com|:)ared w ith the great man-like apes. They are all, on the other hand, 

 inferior to the similar bram regions of li\ ing races. 



THE PROBABI L: D'>\AMIC FACTORS 1NDLCIN(; BKAIN Di:\ ELOI'MEN I IX 



PI I IIECANTHROPUS ERECTUS 



Anv opinion m the endcaxor to estimate w hat d\ namic lactors induced 

 the acKanced brain de\'elopment in ijitheeanthropus nuist needs be based 

 upon conjecture. 1 he major somatic \ariants m primate organization express 

 themselves m the mode and posturt' ol locomotion, in the diilerentiation ot 

 the foot and the specialization oi the hand. To the reactions and interactions of 

 these variants tlu' primati' brain has made delinite res|)onses. The cerebral 

 area most sensitive to and most consistently allected by such modilications 

 has been the paru'tal lobe. This region rej^rcsents those activities engaged in 

 sensing the body both in its axial and appendicular parts. In primates the 

 axial segments ha\X' a greater structural lixity than the limbs whose Junc- 

 tional adaptations ha\e manilested a lar wider range ol adjustment. In 



