882 MAN 



follow that ihc sensory clcniands of a fool so sjx'cializcd as to supijort the 

 body on the ground in the upright posture, thus freeing the hand for eon- 

 strueti\e and aequisitive purposes, called upon the brain for its supreme 

 de\eIopnient in the ])arietal lobe. 



Simultaneous with the expansion in kinesthetic sensibilitx', the motor 

 areas of the cerebral cortex ha\e enlarged. By their extension the\ have 

 increased their capacity for the creation of more numirous and xaried 

 motor patterns. They have gradually dexeloped all of the motor lormulae 

 essential to the almost innumerable skilled manipulations of human hands. 

 Much emphasis has been laid upon the expansion of the sensory portion ol 

 the brain, which may thus seem to pla^' the leading role in dc\clopment. 

 But motor and sensory expansion have gone hand m hand. These two 

 factors are inseparably connected. They appear to be but ditlercnt phases ol 

 the same process, namely, the conversion of energy through the agenc\' of 

 animal organization. The stream of impulses which Hows m Irom the outer 

 world by the avenues of the senses is transformed into the specific energy 

 characteristic of each form of animal life and finally transmitted to the ellec- 

 lors where it appears again in specilically purposive reactions. The intricacy 

 of the apjKiratus for the intake and that for the output \ary directl\ w ith the 

 complexity of reaction. The\ are both, therefore, parts of the same energy- 

 transforming mechanism. It is impossibk' to consider the sensory organiza- 

 tion of the brain apart from the motor. This applies to all t\[)es ol sensibilitx'. 

 The t'\|:)ansi<)n in \ isual capacity indicated by growth in the occipital lobe 

 supports this view. For as \-oluntary acts became capable ol more etlective 

 performances, visual functions were increasingly more necessary to their 

 acquisition and control. Hearing, as the instigator and guide ol new motor 

 progress, may seem to carry less responsibillt \ than the other senses except 

 in one transcendent particular. Auditory fuiution made |jossible the recog- 

 nition and imitation of the inaiu' xoices of nature. It linallv became the guide 



