8o8 MAN 



of Rolando (NR), upon \\ host' oLitcr margin is tlu- descending trigeminal 

 tract (Trd). A few scattered collections of gray matter in the column of 

 Burdach represent the caudal extremity of the accessory nucleus of 

 Bhinienau, also called tin- lateral nucleus of Monakow. 



The circumferential and intermediate zones contain as heretofore the 

 two ascending spinocerebellar tracts (Fie, Gow) on the periphery, and 

 mesial to them the rubrospinal, s[jinothalamic and Deitcrso-spinal tracts 

 (DT, Rst, Spt). 



LEVEL THROUGH THE MIDDLE OF THE INFERIOR OLI\ARV BOD'*' (FIG. 345) 



At this level the changes in the external conhguration arc those incident 

 to the o[)ennig of tlu' tourth \cnlricle and the appearance of the inlerior 

 oh\f in its full development. The dorsal aspect of the section has increased 

 in Its diameter corresponding to the opening ol the veiitricLilar space. In 

 a similar manner the \entral diameter has increased due to the appear- 

 ance of the inferior oli\ary body. Occupying their usual position in the 

 ventromesial portion ol the section are the two pyramids separated by a 

 wide ventromedian sukus. Along the \entral margin ol the |:)yramid a nuclear 

 mass has made its ap|jearance, the nucleus arcilormis. Dorsal to the 

 pyramids is the collected mass of axons h)rming the mesial lilk't ( M I ), 

 to which a number of internal arcuate hbers are still making their way from 

 the cephalic extremitx of tht' nucleus cLineatus. The inferior (liivary nuch'us 

 has its characteristic human ap|)earance. It is distinctl\ outlined and much 

 convoluted in form, with its two accessor\- olixarv elemi'iits, the dorsal 

 accessory obve ( DO) and the mesial accessory oli\e (VO), adjacent to 

 it. This increase in t hi' xolume, in the delinitioii and in the degree ot con- 

 volution of the inlerior oli\t' carries this structure to its highest degree of 

 dilferentiation seen in mammals. Slowly and b\ progressive stages this 

 structure has advanced through all intermediate lihases from the lowest ol 



