MR. J.L. CLARKE ON THE INTIMATE STRUCTURE OE THE BRAIN. 289: 
forward to the pons, where some of them, after running round the root of the fifth 
nerve (Z') plunge into its substance, while others are lost amongst its transverse fibres at 
W'. Both these sets of fibres are joined by others, which also spring from the fourth 
ventricle, but pass beneath the restiform body, and emerge at Y', decussating in their 
passage with the roots of the auditory nerve (Z), as represented in the figure. These 
fibres for the most part run toward W', where they are often continuous with a very 
prominent bundle of the pons. Above the auditory nerve a few more fibres (X') pro- 
ceeding from the fourth ventricle curve round the restiform body as it turns upward, 
and are lost on the middle peduncle of the cerebellum. These fibres are joined by others 
proceeding from under the restiform body at its junction with the middle peduncle. 
(35) The whole of the fourth ventricle and most of the parts that I have just been 
describing, are covered with a layer of columnar epithelium-cells which are shorter than 
those around the canal of the spinal cord, but, like them, they give off from their tapering 
ends a multitude of fine fibres which run in different directions through the subjacent 
tissue. At the lateral parts of the ventricle, the epithelium frequently assumes the form 
of a thicker membranous layer, which springs chiefly from the grey substance lying 
in the angle formed by the divergence of the vagal nucleus and the posterior pyramid, 
and sometimes from the vagal nucleus itself, upon which, as also shown in transverse 
section, there is often a small heap of epithelium-cells (fig. 21, Plate IX. t'"). After 
winding outward round the posterior pyramid and restiform body, the membranous 
layer frequently spreads over the roots of the glossopharyngeal and vagus nerves, mat- 
ting or joining them firmly together. Above, it is continuous with the general epithelial 
layer of the ventricle, and extends over the auditory nerve and side of the flocculus. 
When carefully peeled off from the side of the medulla, it is found to be firmly attached 
to the grey substance, between the vagal nucleus and posterior pyramid, by a multitude 
of fibres, which are the processes of the epithelial cells, and which on removal leave a 
corresponding number of minute perforations, giving to the surface a finely dotted 
appearance*. 
Of the Auditory Nuclei and Nerves. 
(36) I have already described the morphological changes that take place from below 
upward in the formation of the nervous centres which give origin to the auditory 
* The membranous layer of epithelium above described is evidently the “ membrane nerveuse ” described by 
Fovtixe as springing from the auditory nerve to spread over the whole of the ventricle and into the cerebellum. 
“ C’est de cette membrane,” he continues, “ que se detache la lame nerveuse qui unit au nerf auditif le petit 
lobule suspendu au-dessus de lui (the flocculus) ; a cette membrane emanee du nerf auditif se rattache encore 
la lame grisatre elevee de ehaque cote du calamus scriptorius” (the vagal nucleus). He considers the stria: 
medullares as only thicker bundles of the fibres which spring from the auditory nerve and extend into this 
“ nervous membrane.” “ Les tractus blancs, les tractus gris remarques a la surface du plancher du ventricule 
cerebelleux et signales comme des racines de l’auditif ou comme un ganglion de ce nerf, ne sont que des fais- 
ceaux plus forts parmi ceux qui du nerf auditif se portent a la membrane nerveuse parietale du ventricule.” 
Fovnce, Traite complet de l’Anatomie, &c. du systeme nerveux cerebro-spinal, pp. 503, 504. 
2 s 2 
