58 THE LOWER PRIMATES 



pontile fibers, however, cross the midline and recei\e their rehiy in the 

 contralateral pontile nuclei whose axons in turn pass into the middle cere- 

 bellar peduncle. This peduncle extends into the cerebellum and its fibers 

 finally ramify among the various lobules constituting the lateral cerebellar 

 lobes. By means of the pallio-pontile fibers the major functional divisions 

 of the cerebral hemispheres establish direct communication with the lateral 

 lobes of the cerebellum. Experimental and clinico-pathological observations 

 warrant the opinion that these connections are essential to proper coordi- 

 nation in the more complex motor performances of the animal. The 

 pathway between the cerebral cortex and the cerebellum, in a functional 

 sense, parallels the conduction tract which conveys impulses necessary to 

 the voluntary control of action. The latter pathway provides for the trans- 

 mission of nervous energy involved in the purpose and pattern of the act to 

 be performed. This includes the incentive, initiation, design, direction and 

 ultimate inhibition of the act. The pallio-pontile connections provide for 

 concurrent impulses which regulate the coordinative and postural attributes 

 necessary to the execution of such voluntary performances. 



The slight degree of development in the transverse fibers of the pons, as 

 well as in the pontile nuclei and the middle cerebellar peduncle in lemur, 

 points conclusively to a motor organization capable of but a limited range and 

 variety of the more highly synthetized voluntary performances. This fact is 

 corroborated by the rather feeble development of the pyramidal system. In 

 this sense the pons Varolii and its several constituents may be accepted as 

 an index of the extent to which the cerebral cortex has developed. They 

 provide a structural basis for estimating the range of adaptation and degree 

 of volitional adjustment of which the animal is capable. 



The position of the cerebellum is similar to that of the lower levels, 

 and the cross section shows especially well the medullary vestibule consist- 

 ing of all the fibers assembled from the middle and inferior cerebellar pedun- 



