822 MAN 



peduncle corrcsponcl In niiiuile detail In this area in all ol the lower prhiiatcs. 

 In none of" them, however, is the pro|)ortion ol the superior eerehi'llar 

 peduncle so great as in man. Judged b\ this index, it is e\KKnt that eoordina- 

 tive control over the muscles has increased in |)roporti()n to the acquisition 

 of skilled performances made effective by the human hand. A certain number 

 of fillers from the sLiperior peduncle extend into the roof of the ti)urlli 

 \entricU', and man\- of them doubtless assume this position to accommodate 

 the increasing volume of this pathway. For tin- most part, howe\er, those 

 filjers seen in the roofplate belong to the cerebellar commissures. 



Lateral to the peduncle is a thin la\er of lightly myelinized libers 

 which constitute the tractus uncinatus of Russel. This fasciculus forms 

 a part of the juxtarcstiform body and associates the vermal portions of 

 the eerebelhim with nuclear areas in the region of Deiters' nucleus. L\'ing 

 upon tlie |X'ripher\' of the narrow zone forming the tractus uncinatus are the 

 myclinized libers of the ventral spinocerebellar tract (Gow) pursuing its 

 course to the Ncrmis of tlu- cerebellum. These conditions in the neighborhood 

 of the superior cerebellar peduncle deserve special comment since they 

 maintain an invariable arrangement throughout xhv primate series. They 

 have varied onl\ in their jMd|>()rtions, the lower forms showing a less highly 

 developed superior cerebellar peduncle and a much more extensive zone 

 corresponding to the tractus uncinatus of l^ussel. Tlu' fibers composing the 

 \entral sjiinocerebellar tract follow their latlu'r circuitous route to the 

 vermis, maintaining about the same proportions throughout the series, it is 

 dillicult to estimate their actual xohinu', but if anything they ma\ have 

 decreased in man. 1 he increasing size of the superior cerebellar pedunck' as 

 contrasted with llu' lelatively decrt'asing size of the tractus uncinatus pro- 

 duces the x-ariant in the arrangement of this rt'gion. Since the uncinate 

 tract of Riissi'l is part ol'tlu- iuxtari'stilorm bod\, it represents an acti\ity 

 connected with the intrinsically primiti\e liinetions of tlu' cerebellum, its 



