SIM I A SAT\RUS, THE ORANG-OUTANG 529 



Till' basis of till' c-iTi'hral pcdLincli' iCP) is (.■ntiiclx nu'cliillai\ . It 

 contains tlu' bundles of libers which make up the pxramidal tract and 

 tlu' palllD-ponto-cerebellar liber s\ stems. Nowhere in tlu' brain is the 

 relative importance of iiln'r systems more clearly indicated than m this 

 instance. These two s\stems, botli arising in the cert'bral cortex, both 

 e\pandin<i; in volume, size and capacity as the cerebral cortt'x increases in 

 the exolutional sense, both concerned with the eUcrent conduction ot ncr\c 

 imi:)ulses known to be closely associated with the regulation ol motor per- 

 rormanccs, exceed in size all other similar systems ol the neuraxis. Incre- 

 ments in the size of the basal portion ol' the cerebral ]X'duncle are in direct 

 proportion to expansions of areas m the cerebral cortex, j-'roiection libers 

 arisin<i in the neopallium, as, for exampk-, those constituting tlu' |)\ramidal 

 system as well as thosi' enterin<i into the formation ol the pallio-ponto- 

 cerebellar system, denote the ik'o kinetic capacit\ of the animal. 1 he e\ idence 

 allorded b\ the increased xolume of the cerebral peduncle is suscei)tii)lc of 

 but a sin>ile interpretation, nanu'l\, that expansion has taken place in 

 direct proportion to extensions m beha\ loral perlormance, due to the acquisi- 

 tion of more complex, more numerous and more xaricd motor acti\itics. 

 This phyletic history of the cerebral peduncle furnishes testimony in tavor 

 of a progressi\'c cxolution throughout the primate order. 



At the lateral extremitx of tlu' ri'ticular formation is a pronounced 

 elevation, the mesial jicniculate body l^Alf^bj, which recci\es some libers 

 from the lateral lillet. 



From the functional point of \ it'w this lex el signilics certain adxances 

 in the \isLial sense, which appear in the tendenc\- to accjiiire more capacious 

 areas for the extension oi' \ ision w ithin its ow 11 s[)heri' as well as its associa- 

 tion with sensorv impressions in other spheres, such as hearing and body 

 sense. This midbrain lc\el also dcnotts the |:)rogress in the exact conjugation 

 of ocular movements for the purpose of binocular and stereoscopic vision. 



