I\TF,K\A1, SI lUCTLRF. OI- TIIF. BK\i\ SIFM 1003 



stock whosf inluTt'iU triukiu-ics wcrr not only c|n;Klnmianal but were iLirthcr 

 conditioned by tlie addition of a tail which augmented tiie stream ot allerent 

 impulses from the caudal portions ol the body. Ciraduall\ tiie tail became 

 recessive, lost its prehensile or balancing function, and hiially disappeared. 

 During this ])rocess the lower extri-mities, and particularly the feet, dilleren- 

 tiated for the purpose of supporting the bod\ m tlu' upright position. It 

 was, h()\ve\er. the progressive adaptixe de\clo]:)ment m the u|i|3er extremity 

 which gave linal ]:)reeminence to the cuneus because this structure rejjre- 

 sented tlu' i>ro])rioce])ti\e inllux arising from the most ellicieiit organ ol 

 construction and analwsis yet de\eloped b\ the \t'rtebrate kmd, tlu' human 

 hand. 



The relative proportions of the third element of lln' dorsal sensory 

 field, the nucleus of Rolando, are al.so significant. It is mteresting to note 

 that this nucleus has diminished in al! of the primates as compared with the 

 lower mammalian t\ pes, such as carnivores or ungulates. To some extent a 

 similar diminution may be observed in contrasting the lowfr jjrimate lorms 

 u ith those standing nearer to the uppir extremity ol the order. I he decrease, 

 howex er, is not so impressive as to constitute one of the outstanding features 

 in the transitional changes incident to e\'olutional adaptation. Such change 

 as does appear depen<ls upon the fact that the face and head have ])rogres- 

 sively become less im])ortant as specialized areas for guiding the course ol 

 locomotion. Their ollices ha\e largely In-vn superseded by the pronounced 

 development of the hand which has taki'ii upon itself many responsibilities 

 as the chief explorir in the en\ironment, at least m thos<,- cn-eumstances 

 demanding actual contact with objects. When com]>aricl with the progres- 

 sixely expanding cuneus, the nucleus of Rolando, together with the descend- 

 ing trigeminal tract, stands out all the more conspicuously because it has 

 not kept pace with the expansion w hich has so strikingly allected its imme- 

 diate neighbor in the dorsal sensor\- held. For iust as the cuneus, which 



