INTERNAL STRUCTURE OF TME BRAIN STEM 1021 



stnictions ol the poiililc inalci li'iw a still niorc ifalistic idea ol tlicprogrcs- 

 sivc incTenu'iit which thry ])r(.'srnt m this series. 



NeOKIXESIS and DE\ELOiniI£\ I OK THE I^'oOI IN THE AsSlMPTION OF 



THE Erect Posit he. W hile ihi' siuniheanee ot manual dillereiitiatiOn may 

 be easily appreciated m eiHinectioii with t he progrcssivecxtensions in the realm 

 of neokinesis and esi)eeiall\ in relation to tlie expansions ol tin- pontile nuclei, 

 it should not be o\erlooked that the highest degree of manual adaptability is 

 dependent upon an ec|uall\ high specialization ol the loot. Asa matter of hict, 

 the hand in man is less specialized structurall\ than in man\ of the apes. It is 

 the extreme specialization of the human loot which imparts to the hand its 

 real functional opportunit\ to establish manual d 1 11 eren tuition as the supreme 

 achievement of ncokiiu'tic progrt'ss. The apekmd, clinging persistentlx' to its 

 quadrumanal type of organization, resisted that decisive mlhunce which 

 began to shape the human loot. Their conser\atism was epoch-making. It 

 elTectuallN debarrt-d them Irom an\ connection with tlu' human lamily. It 

 was the parting of the wa\s which witnessed the beginnings of a new race 

 ccjuipped to stand upright upon two Icet and use two Iree hands m the strug- 

 gles of life. 



What the pontile nuclei re\ cal ol this ])rocess, the cerebral peduncles 

 still lurther illuminate. The progressive de\ elopmeiit ol tlu' i)etluncles may 

 be seen almost without aid of mensuratioiial methods. There is, however, 

 marked disparity in \ohimetric exi^ression between the cerebral peduncle of 

 the marmoset, whose ]:)lanimetric cot'lllcieiit has a \alueol 10 hundredths and 

 that of man, w here its value is a little less than 30 hundredths. Between these 

 two extremes are all of the intermediate grades indicating progressive incre- 

 ment. Since the cerebral peduncle comprises all of the libers arising Irom the 

 motor area and constituting the pyramidal system, as well as all of the fibers 

 forming the pallio-pontile system, its size accurately rellects the degree of 

 ex'pansion in the cerebral hemisphere. 



