I0I4 EVOLUTIONAL MODIFICATIONS 



the neuraxis in the aflerent and eflerent conduction of impidses over its long 

 projection systems. It is for this reason that e\en the slightest increase in 

 this system of fibers must be regarded as significant of expansion in the func- 

 tional capacity which it represents. Upon comparison, the difference between 

 the planimetric coefTicients of the pyramid in the marmoset and man is 

 represented only by twelve hundredths increase in fa\or of the human motor 

 system. Such disparity as this appears relati\ ely small in comparing these 

 two vastly different primates. But when the pyramidal condensation is 

 viewed as the functional representative of large areas of cortex, the pyramid 

 stands out in man in striking contrast to the corresponding system of the 

 lower primates, and manifests the undoubted influences of an evolutional 

 process. 



The increase of the pyramidal system, however decisi\e it may be in its 

 bearing upon the development of the neokinetic functions, is relatively less 

 conspicuous than the expansion of the pons Varolii. This applies most partic- 

 ularly to the pontile nuclei. Two facts show an intimate connection between 

 these nuclei and neokinesis: first, they ser\e to relay fibers from several 

 areas of the neopallium, and second, the axons arising in them terminate 

 in the lateral lobes of the cerebellum. Interpreted in the light of the function 

 which the pontile nuclei serve, this linking of the cerebral hemispheres with 

 the lateral lobes of the cerebellum is in the interest of the coordinative activ- 

 ities expressed in the appendicular musculature. This conclusion is justified 

 by the fact that experimental and clinico-pathological evidence points to 

 the lateral lobes of the cerebellum as an acquisition of the central nervous 

 system for the distribution of coordinative impulses to the muscles of the 

 extremities. The lateral lobes differ from the vermis since the latter is partic- 

 ularly concerned with the distribution of coordinative impulses to the axial 

 musculature of the trunk, neck and head. From the functional specialization 

 of the neopallial areas participating in the important communication con- 



