ioo6 EVOLUTIONAL MODIFICATIONS 



represents the arm and hand, has gradually gained preeedenee m size and 

 conducting capacity (ner xhv elava which represents the leg and foot, so the 

 dorsal representative of manual dillerentiation gamed ])reemmence ovc^r the 

 nucleus of Rolando and its accompanying libers, the descending trigeminal 

 tract. 



E\OLLTI()NAL ADVANCES IN NEOKINESIS WITHIN IHE PKIMArEOKDEK 



if these elements of the hram, including cranial iuicUm, reticular lorma- 

 tion and nuclei of the dorsal sensory field, express much that is mherentl\ 

 archaic. If tluA retain in large measure the primordial characters of neural 

 organization iinoKed in such essential tunctions as respiration, cardiac 

 acti\Ity and digestion, the control ot deglutition and mastication, the 

 mechanism of balancing, the transmission of propri()cepti\-e iniijulses 

 from the head and extremities and the regulation ol the ocular muscles, 

 there are also elements in the brain which arc much more responsive to the 

 inlhiences of adaptat ion. The structure of these elements possesses a plasticity 

 cspcciall\ sensitixe to the exolutional acKances which characterize the new- 

 sphere ol primate actnity. 



Were it ]:>ossible to summanzt' bnell\ the outstanding transitions 

 through w hich these animals ha\e made their steadx acKance, these features 

 might l)e said to com])rise those s|)ecilic relinements in motor perlormances 

 whicli made progressixc adai)tation jjossible. Hu'\ brought to bear upon the 

 externalizing ca])acity of the animal more complex syntheses ol sensory 

 combinations and ga\e to the execution of muscular action a grcviter range 

 of llexibility. Tht'v pro\ ick'd the incenti\efor the constructixc faculties of the 

 most facile and adaptable |:)ortion of the bod\, the hand, and sublimated in 

 this facilitx tlie powt'rs of selection betwc-eii alternati\c' courses ol action. 

 They added the cjuality of judgnu'iit for manual guidance. 1 he\ im|)artedto 

 deftness those factors of en-atixe imagination w host' culmination is that 



