586 THE HIGHER ANTHROPOIDS 



position of the more ventral ol llic two spinocerebellar tracts ( Gow ), mesial 

 to which are the rubrospinal and spinothalamic fasciculi ( Rst, Spt). The 

 inferior oli\e apj)ears perhaps even more conspicuous at this level than in the 

 one pre\iously described. It shows all ol its characteristics m coiuolutions, 

 definition of outline, size of fundus and richness oi libcr connections. Mesial 

 to it is the dense bundle constitutin<i the central pathway of discriminati\e 

 sensibilit\, the nu'sial lillet ( Ml ), while in the ventromesial jjosition ot the 

 section is tin- massive pyramid ( Py ). A notable addition in connection with 

 the ventral surface of the pyramid is the appearance ol a relatix fly large mass 

 of gray matter, the nucleus areiformis ( Nar). This structure aj^pears to be 

 the caudal extension of the nuclear masses which constitute the pontile 

 nuclei. One of the most striking IcatLircs of the brain stem in the great 

 anthropoids is the increase in the pons Varolii, particularly in its nuclear 

 masses, whose extension below the caudal pontile limits along the \entral 

 surface of the pyramid is expressive of extreme acti\ity in growth. There 

 may be obiections to this interpretation of the nucleus areiformis on the 

 ground of its connections. In reconstruction, however, this nucleus appears 

 to be in direct continuity with the gray matter constituting the nuclei of the 

 pons. It appears onl\' in those primates in which the [jons Varolii has show n 

 that exuberant expansion which dcNcloixs m direct consec|uence of growth in 

 the cerebral hemisjiheres. 



LEVEL OF THE CEREBELLAR NUCLEI (FIGS. 260, 26 1 AND 262) 



At this lew I the most prominent lent u re is tlu- appearanct' ol the nucleus 

 deiitatus 1 NDt) which is situated m tlu' nu'dullar\ \estibule of the cere- 

 bellum. At this \v\v\ also the cerebellum occupies a ])()sition alio\f the 

 roof of the fourth \entricle, into theca\'it\ of wliieh projects a [portion of the 

 inferior \ermis (Ver). The ca\it\ itself Is more s|)acious than in pre\'ious 

 sections. 1 he lloor of the ventricle is broader than elsewhere because of 



