1036 EVOLUTIONAL MODIFICATIONS 



in man this ligurf rises to the vahK' ol ()(> piT cent, a total ciiiKTciice oi "4 

 hundredths between the two extremities of this order, j-roni sueh a ditlerence 

 in values, it may be inferred that the lunetional importanee of stereoscopic 

 \ision lias increased most j^artieularly in proportion to tlie degree of apphca- 

 tion of tlie hand m the execution (j1 the most highly organized motor 

 perlormanees. 



The motive running through this entire j^roeess ol dex'elopment is not 

 dillieult to appreciate. Some parts ol the brain, essentiall\ progressive in 

 their tendencies, ha\e reacted by what seems to be an almost enthusiastic 

 response. They have grown m their proportions and gained preeminence in 

 their mlluence. This is especially true ol the neopallium, ol the p\raniKl and 

 pons, ol the cerebral peduncle, ol the lateral lobes ol the cerebellum and the 

 structures connected with them. Some parts ol the brain ha\'e mamlested 

 greater conserxatism in their adaptive reactions, as, for example, the centers 

 of the balancing nu'chanism, or those lor the transmission ol other proprio- 

 ce]3ti\c' impulses. Still other parts, like most ol the cranial iier\e nuclei, 

 ha\e been actuallx' resisti\e in their greater ]3hyletic stability, although 

 even the\ ha\e not escaped the progressu'e inlluences arising from such 

 acKanced acc|uisitioiis as the development ol articulate speech, ol emotional 

 expression and ol stereoscojjie vision. 



A complete tabulation of the plaiiimetric coellicieiits lor all ol the 

 structures which ha\e been discussed in their exolutional relations is 

 appended on page 103". The coellicieiits lia\t' been so arranged as to iiWv 

 them their sequential order of importance whh relerence to the evolutional 

 process wiiich they indi\ iduallx rtpresc-nt. It will lie obserxcd that the\ fall 

 naturall\- into three groups those ]3ri'emineiitl\ concerned witli the ex]:)an- 

 sion in the neokinetic sphere, those to some extent intimatelx connected 

 \Mtli this expansion and those representing archaic structurt's which have 

 ielt m a nuich more remote manner the inlluences ol neokinetic de\elopment. 



