SUMMARY OF STRUCTURES 275 



the corona radiata, or in the internal capsule where they become convergent 

 toward the cerebral peduncle, are not discrete enough to produce exclusive 

 involvement of the pallio-pontile axons. Thus it is that no pure disturbance 

 involving this system has yet been observed. Either the motor system or 

 some part of the sensory system is simultanecnisly implicated by the lesion, 

 and so adds elements which raise doubts as to the specific function of the 

 pallio-ponto-cerebcllar fibers. Experimental lesions are complicated by 

 similar difficulties. Neither of these sources of infVirmation has, therefore, 

 contributed as much as might be desired in revealing the functional activities 

 of this system of axons. On the other hand, the increase of this system in 

 animals capable of highly complex performances bespeaks a function which 

 has a capacity for expansion directly proportional to the evolutional develop- 

 ment of the cerebral hemispheres. 



The origin of these fibers in the cerebral cortex, their relay in the pons 

 Varolii, their termination in the lateral cerebellar lobes, declare them to be of 

 utmost importance in some phase of neural activity whose mechanism 

 ultimately depends upon the cerebellum. This mechanism at the same time 

 has as its essential coadjutor the controlling influence of the cerebral cortex. 

 Whether it be finally decided that the functional capacity of the pallio- 

 ponto-cerebellar system is primarily in the interest of coordination for the 

 performance of complex skilled acts, or whether it is shown that there exists 

 some other reciprocal relation between the cerebellum on the one hand and 

 the cerebral cortex on the other, is a question for further investigation to 

 decide. In either case the pontile nuclei serve as a relay for a great system of 

 fibers arising in the neopallium. They show progressive expansion in propor- 

 tion to the evolutional development of the endbrain. Such expansion goes 

 hand in hand with the acquisition of more complex, more numerous, more 

 varied \'oluntary performances, capable of producing a greater continuity 

 in action. That motor activities characterized by such qualities as these are 



