274 THE LOWER PRIMATES 



set have not attained the degree of speeialization that eharacterizcs lenuir or 

 mycetes, they still have developed sufficient capacity for complex skilled 

 performances to necessitate relatively extensive pontile nuclei. 



THE PALLIO-PONTO-CEREBELLAR SYSTEM 



By means of the relay already referred to in the pons, the pallio-pontile 

 system is continued into the cerebellum. This entire collection of fibers con- 

 stitutes what is termed the pallio-ponto-cerebellar system. As these libers 

 take their origin in the cerebral cortex, they are spread out much m the 

 manner of a fan, becoming convergent as they approach the internal capsule 

 and cerebral peduncle. In their termination, also, they again spread out in 

 relation with the lateral lobes ol the cerebellum. Thus, the pallio-ponto- 

 cerebellar system has in relation with it two conspicuous fan-like radiations: 

 one at its origin in the cerebral cortex, another in its termination in the lateral 

 lobe of the cerebellum. This is a morphological fact of much significance, 

 clearly indicating as it does the many regions ot the cerebral cortex which 

 are connected with all areas of the lateral lobe of the cerebellum. Further- 

 more, as the cerebral hemisphere increases in size and prominence during 

 the course of evolutionary expansion, this pallio-ponto-cerebellar system 

 likewise gains in volume. It contains a greater number of fibers in those 

 animals possessed of large hemispheres with well-delined lobation than in 

 those species in which lobation is more inconspicuous. It follows that in 

 proportion as the number of fibers arising in the cerebral cortex is large, so 

 also are the pontile nuclei. 



Functional Significanceof Pallio-ponto-cerebellar Fibers. Clin- 

 ical and pathological conditions have not as yet yielded satisfactory evidence 

 concerning the functional significance of these pallio-ponto-cerebellar fibers. 

 The reason for this deficiency is not far to seek. Lesions in the cerebral 

 hemisphere near the surface of the cortex where these fibers take origin, in 



