THE MEDULLA OBLONGATA. 233 



the eighth nerve is thus subdivided into two principal parts, known 

 respectively as the dorsal or lateral and the ventral or mesial roots. 

 The fibres of the dorsal root inclose amongst them numerous ganglion 

 cells ; this root becomes the cochlear or true auditory division of the 

 eighth nerve. The ventral root, which becomes the vestibular division 

 of the eighth nerve, is connected with a mass of grey matter mesial to 

 the restiform body (n.VIII.p.\ and also with a nucleus (n,VIII.ac.) 

 lying ventral to the restiform body, and known as the accessory 

 nucleus. The reticular formation still occupies the greater part of each 

 lateral half of the bulb between the grey matter at the floor of the 

 fourth ventricle and the pyramids (py], and a small portion of the 

 olivary nucleus (o) may still be seen, as may also the upward continua- 

 tion of the grey matter of the tubercle of Eolando ; this is intimately 

 connected with some well-marked bundles of nerve-fibres, which are 

 passing up to the pons to join eventually the root of the fifth nerve 

 (Fa). The restiform body (c.r.) is formed partly of the fibres of the 

 direct cerebellar tract of Flechsig of the same side, which are derived 

 below from the cells of Clarke's column, and pass above into the middle 

 lobe of the cerebellum, partly of fibres from the opposite olivary 

 nucleus, and partly of fibres from the olivary nucleus of the same side. 

 These pass to the cerebellar hemisphere mainly. It also receives some 

 fibres from a nucleus which lies just outside the grey matter of the 

 funiculus cuneatus, and is known as the outer cuneate nucleus 

 (fig. 258, n.c'.). 



Pons Varolii. A section through the middle of the pons Varolii 

 (fig. 263) shows very much the same arrangement of grey and white 

 matter as that which is met with at the upper part of the medulla 

 oblongata, but the general appearance of the section is much modified 

 by the presence of a large number of transversely coursing bundles of 

 nerve-fibres, most of which are passing from the hemispheres of the 

 cerebellum to the raphe (fibres of middle peduncle of cerebellum). 

 Intermingled with these bundles is a considerable amount of grey 

 matter (nuclei pontis). The continuation upwards of the pyramids of 

 the medulla (py) is embedded between these transverse bundles and 

 separated by them from the reticular formation. The deeper transverse 

 fibres, those which are nearest to the reticular formation, belong to a 

 different system from those of the middle peduncle. They form what 

 is known as the trapezium (fig. 263, t) ; a collection of fibres which perhaps 

 connects the superior olivary nucleus (see below) of one side with the 

 accessory auditory nucleus (fig. 262, n.FIII.ac.) of the other side. The 

 olivary nucleus is no longer seen, but there are one or two small col- 

 lections of grey matter much more conspicuous in some animals than in 



