Chai'ti:k .Will 



COMPARATIVE SUi\L\lAR^ OF STRUCTURES HAVING 



EVOLUTIONAL SIGNIFICANCE IN THE BRAIN STEMS Ol" 



THE HIGHER ANTHROPOIDS 



A Criliccil C()m])uns(in of ihv Pxramulul Trad, Olivary \iuli'us. Dorsal 

 Setxsory Suclci, \'cstil)uUn\ Ccrchcllar. Red and Pontilt' \uclci, ll.U' Midhrain 

 Colliculi and ibt- ()culi)m<>l<ir Dtcussalion: Their Evolutional Sii^nijicancc in 



Rclalion Id Behavior 



I. The Pyramidal Tract in Relai ion to the VoLLNTAR^ Conirol of 

 THE Extremities with Especial Reference to the Hand 



"^1 IE p\ raniiclal system as an iiuk'x of Noliliona! control allorcls a con- 

 sistent guide in estimatinji; certain hehaxioral dillereiices among the 

 ]jiimates. This system oi lihers is a distinctlx mammalian acc|iiisi- 

 tion. It rcjjresents a new acKeiiture in motor organization. In then- progres- 

 sive dexelopment the primates lia\t' utilized this endowment to greatest 

 ad\antage. The signilicance of the p\ lamidal system is rt'lati\ely simpli'. It 

 introduces a new factor into the ancient neural control ol the muscles wliK'h 

 imparts to their primordial acti\ities a more e\tensi\x' adaptability. In 

 realitx this new mammalian s\stem remodels tlu' old sj^herc ol \ crtebratc 

 heha\ lor. The animal possessed of it manifests new combinations m ri'action, 

 begins to act with some e\ ideiice of a wider selection between man\ possible 

 courses ot motor response. 



the NEOPAI I UM Ol HIE ENDBRAIN 



In itseli the p\ ramidal s\stem, however, is but the sublimated repre- 

 sentation of the most rect'nll\ acquired, most expansible portion ol the 



699 



