9-4 E\OLLTIONAL MODIFICATIONS 



All of this chanee from i. .nething approaching convexiU" 



in t . e is the result of expansions in the 



rest of extending the capacit\" of visual function. 



In. vHum grves evidence of an expanding 



process. In _ martially covered by the caudal p>oIe of 



:.e occipital lobe is poorly developed. This 

 con-^ iracteri; .e more primrtr^e hemispheres in the carniAores 



: _ :es. ^ et even in lemur the tentorial surface has a definitely gabled 



nee. The superior vermis is a prominent element, while the inferior 

 vermis app>ears much more as a surface eminence than in the higher species. 

 In the marmoset, the ultimate primate condition obtains in that the upper 

 cerebellar surface is entirely concealed by the overlying occipital lobe. 

 The tentorial surface also shows a marked gabling with an extremely high 

 p :ts vermal region. A similar condition exists in mycetes, both 



on the tentoria. ccrpital surfaces. In all three of the lower primates, 



the lateral expansion of the cerebellar hemisphere is relatively slight. The 

 movement toward development in this p>ortion of the brain first becomes 

 evident in the intermediate primates, although even in them the vermis 

 remains a most conspicuous feature of cerebellar organization. It is not until 

 the great anthropoids are reviewed, that the real changes in cerebellar expan- 

 sion become apparent. In these instances, while the gabling of the tentorial 

 surface is still fairly prominent, there is a distinct tendency for the vermal 

 ridge to lose its high elevation, for the vallecula to become pronounced and 

 for the 'i.ermi': to fall off in comparison with the lateral lobes. Finally in man, 

 t rface is almost flat, the vermal ridge inconspicuous and the 



vallecula so deepened that the inferior vermis is almost lost to \ iew within 

 it. The process which has progressively advanced in the development of the 

 cerebellum is obvious. It is characterized by expansion of the lateral lobes 

 without proportional increase in the vermal portion of the organ. Since the 



