THE GRAY MATTER. 607 



but with the other, true, cranial nuclei ; and in any case we must probably 

 consider the median division of the auditory nucleus, not as a nucleus in the 

 sense in which we are now using it, but rather as a secondary connection 

 within the bulb. 



When we trace the ventral root, vestibular nerve (Fig. 134), inward, we 

 find that it makes, according to most observers, no connections at all with the 

 accessory nucleus ; and that it passes (Fig. 134, F///.) to the median side of the 

 restiform body, between it and the ascending root of the fifth nerve, and so 

 reaches the lateral division of the nucleus, in the large cells of which most 

 at least of its fibres are said to end, and which, therefore, may be regarded 

 as the nucleus of the ventral root. On this point, however, all authors are 

 not agreed. The lateral auditory nucleus, with the fibres proceeding to and 

 from it, lying as they do to the median or inner side of the restiform body 

 proper, are sometimes spoken of as the median or inner division of the resti- 

 form body; and from the nucleus a considerable number of fibres pass up 

 with the restiform body into the cerebellum as a continuation of this 

 " median division of the restiform body." Some authors maintain that these 

 fibres are continued straight on from the nerve to the cerebellum ; but the 

 more recent investigations seem to show that they all make connections with 

 the nerve-cells of the lateral nucleus on their way. These fibres constitute 

 a connection between the auditory (vestibular) nerve and the cerebellum, 

 the physiological significance of which we shall see later on ; we may, per- 

 haps, compare it to the connection between the posterior roots of the spinal 

 nerves and the cerebellum through (the vesicular cylinder and) the cere- 

 bellar tract. 



The other central connections of the lateral nucleus are, like those of 

 the accessory and of the median nucleus, complicated and obscure. But we 

 may call attention to a set of fibres which, starting apparently in the acces- 

 sory nucleus, run directly transverse in the ventral region of the tegmentum 

 just dorsal to the transverse fibres of the pons, forming what is called the 

 trapezium (Fig. 134, Tp.). 



Lastly, we may add that the fibres of the peculiar portio intermedia 

 appear to take origin from the accessory nucleus. 



532. The seventh or facial nerve. The nucleus (Fig. 138, VII., and 

 Figs. 133, 134, VII. 7i.) of this nerve (it being borne in mind that the motor 

 fibres for the orbital region (the orbicular muscle, etc.), though they run in 

 the trunk of this nerve, really belong to the third nerve and take origin 

 from the hind part of the nucleus of the third nerve) is narrower in front 

 than behind, reaches from the level of the striae acusticse some distance into 

 the region of the pons, and occupies in the midst of the reticular formation, 

 a little dorsal of the patch of gray matter called the upper olive, a position 

 corresponding closely to that of the nucleus ambiguus. The cells of the 

 nucleus are large, and possess well-marked axis-cylinder processes, which 

 are gathered up at the dorsal surface of the nucleus to form the root. This, 

 rising up dorsally, describes a loop (Fig. 134, VII. #.) round the nucleus of 

 the sixth or abducens nerve, running forward for some little distance dorsal 

 to that nucleus, and then descends again ventrally, passing to the lateral 

 side of its own nucleus, between it and the ascending root of the fifth ( V.a.) ; 

 it thus gains the surface of the brain at the hinder margin of the pons, 

 lateral to the abducens, opposite the front end of the groove between the 

 olivary body and the restiform body. As it thus encircles the nucleus of 

 the abducens, it looks as if it were receiving fibres from that body ; but the 

 evidence goes to show that these fibres simply pass through the nucleus, and 

 do not take origin from any of its cells. 



533. The sixth or abducens nerve. This nerve starts from a compact oval 



