,o2o EVOLUTIONAL MODIFICATIONS 



Those who arc opposed to cliseretel\- diagrammatic and somewhat dofj- 

 matlc allocation of specific functions to circumscribed areas ol the cerebral 

 cortex may obicct to this interpretation. Their objections must I)e received 

 and considered w ith respect. Nor should they be lost sight of in the further 

 exploration of tin- cortex. There already exists, however, so much that is 

 con\incing with reference to specific localization in the neopallium, that 

 many authorities hnd no dillicult\ in attributing to the intermediate pre- 

 cential area a specific function. Whether or not this function ultmiatclx 

 proves to he the regulation of highly skilled motor perlormancis m no way 

 affects tlu' \alidity of the large contribution of fibers which the mtt-rmediatc 

 precentral area makes to the pallio-ponto-cerebellar system. The frontal lobe 

 of the brain is unc|uestionably connected with the lateral lobes of the cere- 

 bellum. Its connection represents some phase in the expression of neokinetic 

 aeti\ ity. W ith certain reservations as to the exact significance of some of its 

 constituents, the entire i:>aifio-])onto-cerebellar system may be accepted as 

 an espeeiall\ reliable index of neokinetic expansion. The relation of the pon- 

 tile nuclei to this system appears in the fact that they are the relay station 

 for the fibers arising in the several lobes of the neopallium and seeking final 

 distribution in the lateral lobes of the cerebellum. If these nuclei manifest 

 augmentation in ]:)assing from tlu' lower to the upper extremity of the order, 

 the inference seems justifiect that the system with which they are connected 

 has been corres]:)ondingly augniented. A progressive expansion of this kind 

 is so ])romiiU'ntl\ demonstrated in the comparison of the primates as to 

 make the pontile nuclei the most significant indicator of the cN'olutionarv 

 process in the brain stem. The planimetric cot'llicicnt of these nuclei in the 

 lemur is j^ 2 hunchx'dths. At the otiu'r e\trcmit\ of the series it is 55 hun- 

 dredths, a gain of 4()'_» hundredths in passing fronrthc lemur to man. in 

 no other structure of the brain stem is there such marked expansion. Recon- 



