p 



TROGLODYTES NIGER, THE CIIIMI^ANZEE 583 



nucleus ol Bluincnau ( N B 1 ). Tlir nucleus of Rolando ' N R 1 1 the substantia 

 gelatmosa tngeninii) is consicleral)l\ less In size than the nucleus ol'Cioll and 

 also less sharpl\ delined inouthne. It has in contact with its outer margin the 

 descending trigeminal tract ( Frd) across whose outer surface pass many 

 ol the libers ol the ascending spinocerebellar sxsti'in 1 bli'l I'litering into 

 the lormation ol the restiiorm body. The intt'rniediate lissure, together 

 w ith the postoli\ar\ sulcus, bounds a slight eminence on the latt'ral surface 

 which corresponds to the |)osition ol the more \i'ntral ol t hi' two spinocere- 

 bi-llar tracts iGow ) mesial to which are situated the ruljrospmai and 

 spinothalamic tracts (Rst.Spt). The reticular lormation iRef) forms 

 tiK' ct'iitt-r ot the section and is pt'iu-t ratc-d by many internal arcuate libers, 

 eiiiell\ those taking origin in the nucleus ol Burdach. These make their way 

 inward toward the raphe, w heri' tlu-\ undi'rgo cU'cussation to enter the 

 mesial hllet 1 M f ). Ventral to the latter is the compact bundle constituting 

 the pyramid (Py ). 



LEVEL 01^ THE \ ESIIBL LAK M CLEI (IIG. 2ji)) 



Here the chief alti-ration in the section is determiiU'd b\ the wide oj:)en- 

 ing of the fourth xcntricle and the ajjpi'arance, in the position previously 

 occupied b\ the dorsal sensory nuclei, of the two \-eslibular nuclei forming 

 the central primar\ stations of the proprioceptors situated in the semicircular 

 canals, utricle and saccule. The central gray matter here occupies its typical 

 position in the lloor of tlu- fourth \i-ntricle and shows certain minor ditlerences 

 from the arrangement of this structure in pre\"ioiis lexcls. In the lirst |)lace, 

 it includes the cei)halic t'\trt'mit\ ol' the h\[30glossal nucleus 1 \hy) as its 

 lil)ers [)ass forward toward tlu' inferior olixc i 10), lateral to which is the 

 cephalic remnant of the dorsal \agal nucleus ( Nvd ). Interposed between 

 the Inpoglossal nucleus and the dorsal nucleus ol the vagal nerve is the 

 well-delined luiclear mass constituting the lower extremitv ol the vestibular 



