THE BRAIN OF MODERN MAN 817 



lum leads to a coiulitiDn of ataxia or (lisarrangcnu'nt in tin- |KTlorniancc' of 

 such mo\ t'liu'iits. 1 lu' act is cmharrassccl i)\ a scries ol irrciiular oscillations. 

 Flexion in one place is o\H'r-cni|)liasi/.e(l and must he counteracted b\ o\er- 

 extension, which ni its turn is extri'nie. 1 hus that plastic skeleton ot posture 

 about which the execution ol each skilk'd act is molded, loses its cohesive 

 support and has every appearance of thorough disorganization. 



The most acti\e agent of skilled |)erlormances in man is the hand. 

 Without siK'h speciali/.ation as this it would be im|)ossible to de\ flop t he 

 range and \arii't\ of complex manual moxcmcnts ol which man is capable 

 and for which the xastlx increased output ol coordmat i\ t' control Ijccomes 

 necessary. Responding to this demand t he lateral cerebellar lobes ha\e show n 

 their ex|)ansioii. It is not to be o\ crlooked, ho\w\i'r, that tlu' lower extremit\' 

 manilests ct'rtain latent potentialities for the de\ elo|jnu'nt ol highl\ complex 

 acts. Not a lew cases are on record m w huh indi\ iduals ha\e been deprn fd of 

 both upper extremities b\ amputation at or near the shoulder. Some indi\ id- 

 uals thus alllicted ha\c so educated the lower extremities and leet as to 

 accjuirt' the control of moNcnu'iits necessary for painting and writing. These 

 moxc'iiU'iUs belong to tlu' group ol acc|uired skilU'd perlormanccs to the usual 

 list of which many others may be added b\ special training as, tor example, 

 those seen in jugglers. The cerebellum thus appears to contain a certain unde- 

 veloped jjotcntiality which, under stress of unusual circumstances, may l)e 

 made available. 



LEVEL OF THE INFERIOR PORriOX OFIIIF PONS \ AROl 1 1 ANIVIIlF EMERGENCE 

 OF THE Sl.MH CKANI Al. NEK\ E, THE NER\T S ABDl CENS (FIG. 34y) 



Here the configuration of the section has undergone considerable modili- 

 cation, due to the addition of massive transverse bundles and other structures 

 pertaining to tlu' pons \ arohi. By the addition ol the pontili' elements, the 

 marked distinction l)etween the basis j^ontis and the tegmentum pontis 



