THE MEDULLA OBLONGATA AND BRAIN STEM 493 



of the tenth nerve, however, are rather coarser and form larger 

 bundles than those of the ninth. 



At the level of the ninth nerve the dorsal and medial accessory 

 olivary nuclei make their appearance. They form, on either side, 

 two isolated flattened grey masses. The dorsal accessory nucleus 

 is flattened antero-posteriorly, and lies just behind the mesial half 



FIG. 384. TRANSECTION OF THE HUMAN MEDULLA OBLONGATA AT THE MID-LEVEL OF 



THE INFERIOR OLIVARY BODIES. 



cH, central tract of the tegmentura ; do, dorso-olivary fiures ; faev, ventral external 

 arcuate fibres ; Fc V, accompanying tracts of the trigeminus ; Ftp, posterior longitudinal 

 bundle ; Hil, hilum of the olivary body ; io, intraolivary fibres ; it, arcuate trigeminal 

 fibres ; IXa, spinal root of the glossopharyngeus ; IXa', accessory bundle of same ; Lm, 

 mesial lemniscus ; m, dorsal longitudinal bundle of Schutz ; Na, nucleus ambiguus ; 

 NarcP, arcuate nucleus of the pyramids ; Ncu, nucleus of Burdach ; Nft, nucleus of the 

 eminentia teres ; NiS, intercalate nucleus of Staderini ; Nit, nucleus of the lateral column ; 

 No, inferior olivary body ; NB, nucleus of Roller ; Nvtd, chief nucleus of the vestibular 

 nerve ; NX, dorsal or chief nucleus of the vagus ; NXII, hypoglossal nucleus ; Oaa, me- 

 sial, and Oae, dorsal accessory olivary nuclei ; Plchm, mesial choroid plexus ; Pol, pontic- 

 ulus ; pt, trigeminal arcuate fibres ; pt', marginal trigeminal arcuate fibres ; Py, pyr- 

 amids ; Ra, raphe ; rt, retrogeminal arcuate fibres ; Sgl, gelatinous substance of Rolando ; 

 Sri, lateral reticular substance ; Trs, rubro-spinal tract of von Monakow ; Tscv, Gowers' 

 tract ; Tst, spino-tectal and thalamic tract ; TVIII, acoustic tubercle ; vcpl, ventral col- 

 lateral plexus ; Villa, spinal root of the auditory nerve ; VIIIc, cochlear nerve ; VIV, 

 the fourth ventricle ; X, vagus nerve ; XII, hypoglossal nerve. Weigert's stain, x 5. 

 (After Marburg.) 



