THE BRAIN OF PREHISTORIC MAN 883 



of motor impulses for the ton<iuc, for tlic larynx, for the lips, cheeks and 

 tliroat Linlil the aiichhie eiu'r>j;y ol the outer world \\as transformed mto 

 spoken sounds of the human \i)iee. Sounds ol this kmd e\c'ntuall\' assumed 

 svmbohe associations with gestures and other movements of tlie body, with 

 ()l)|ects seen or otherw ise pereeixecL The meeption of [luman speech had its 

 structural basis m the hrst and second temporal convolutions whose expansion 

 is at least mdieated m pithecanthropus. These gyres represent the funda- 

 mental sensory elements ol s])eech while the inferior frontal coiiNolution, 

 constituting Broca's area, exercises motor control over spoken language. 

 All of these expansions in the sexeral diflerent areas of the bram are ulti- 

 mati'ly reflected in the dewlopment of the frontal lobe. The cumulatiw efiects 

 of many factors impress themseKes upon this region. The assumption of 

 llie erect posture, the freer use of the hands, the fuller sensing of the world, 

 the acquisition of speech and constructive proclivities, the incentive to 

 ex|)lore and the ability to migrate, combined to broaden human experience 

 and to increase the capacit\' to li'arn therefrom. The part the\' pla\ed in 

 indi\iduahzing human personality, in expanding the powers of selection, in 

 creating tiie foundations of ]udgment and reason is obvious. All of these 

 higher psychic faculties are now attributed to the frontal lobe. 



In the cNolution of structure and beha\ior indicated by the brain of 

 Pithecanthropus erectus, man\ factors ha^"e reacted and interacted. It is 

 doubtless true that no single formula attempting to outline the sequence of 

 events in this process would be w holly satisfactory or correct. Some working 

 program of this kind, howi'\'er, is not objectionable and may be helpful if its 

 hypothetical nature is frankly admitted. The following summary of such a 

 sequence visualizes pithecanthropus as departing from the pronogradc stem of 

 the primates and making decisive advances beyond the anthropoid stage by: 



1. The development of more extensive kinesthetic and motor capacity 



2. The assumption of tlu' erect posture 



