1034 EVOLUTIONAL MODIFICATIONS 



the midbrain, compared with the more eosmopoHtan advantages of the 

 cerebral cortex, became an en\ir()nment too jjrovincial and hmited I'or the 

 ultimate de\'eIopment of vision. Tlie sense of hearing was similarly alleeted 

 in its disposition toward its original mesencephalic allocation, once tlu' 

 neopallium had re\ealed its de\elopmtntal possibilities. Hearing iollowed 

 tile example of \ ision and together they sought new lields for e.xpansion in 

 the lu'misj)iieres ol the endbram. 



The delegation ot auditory and \ isual hmction Irom the roof of the 

 mesencephalon to areas in the cerebral cortex is part ol that process of 

 telencephalization which has pi'ogressed through the mammalian orders. 

 Its obvious purpose was to procure lor these s|)ccial senses more expansi- 

 ble areas lor their elaboration with other types ol sensibility. As in all 

 other instances, the prime object ol such expansion was not mcrel\ the 

 extension ol the s|)ecial sense iiuolwd, but much rather the multiplication 

 of its cajjacities lor c\j)ression. 1 hus, increasing the spheres of vision and of 

 hearing had lar-reaching ellects upon the expansion of neokinesis. The 

 functional increments to the sense ol hearing, in consec|uence ol its neopallial 

 opportunities may be clearl\- w itnessed m the expression of articulate speech. 

 To many other human acti\'itics hearing has bt'conu' essential. The auditory 

 development that leads to the recognition and combination ol sounds in tlu' 

 torm ol music and the ultimate externali/.ation ol such auditory syntheses in 

 the musical |:)rodiictions ol the \()ice or by manipulation ol musical instru- 

 ments reveal tlu' important role which the sense ol hearing plays in the 

 extension ol neokinelic aciiievenunls. Its instrumentalit\ m tlu' j)roccsscsof 

 learning is obxious, for without such auditory assistance it is probable that 

 many of the highly skilk'd performanci's of which man is capable would fail 

 of their complete (k'\-clopmcnl and lack one of the chief stimuli which incite, 

 create and direct them. 



