CHAP. IL] THE BRAIN. 957 



and the bundle eventually ends in front by passing into the 



flossopharyngeal roots. The grey matter from which these 

 bres take origin does not form a denned compact area, is not 

 therefore a nucleus in the sense in which we are now using the 

 term, but is diffused among the rest of the grey matter along a 

 considerable length. The fibres are nevertheless fibres of nerve 

 roots, and the bundle is called the ascending root of the 

 glossopharyngeal, the term ascending being used since it is 

 customary to trace such structures from below upwards, that is 

 from behind forwards ; though since the fibres in question are 

 probably afferent fibres carrying impulses backwards from the 

 nerves to the grey matter, 'descending' would be the more 

 appropriate word. The bundle has also been called the fasciculus 

 solitarius ; and, since its position has been supposed to correspond 

 to that of the area marked out experimentally as the respiratory 

 centre, 361, it has been spoken of as the respiratory bundle. 



The roots of these three nerves then, the bulbar accessory, the 

 vagus, and the glossopharyngeal, all leaving the surface of the 

 brain along the line between the olive and the restiform body, 

 and all so far alike that it is impossible upon mere inspection to 

 say where in the series the fibres of the middle nerve, the vagus, 

 begin and end, spring from three sources, the combined nucleus, 

 the nucleus ambiguus, and the ascending root. 



618. The Eighth or Auditory Nerve. This nerve differs from 

 the other nerves which we are now considering in being a nerve of 

 special sense ; its arrangements are complicated. In a view of the 

 base of the brain (Fig. 108, (7.), the nerve is seen to leave the 

 surface of the brain from the ventral surface of the fore part of 

 the restiform body at the hind margin of the pons as two strands 

 or roots, one of which winds round the restiform body so as to 

 reach its dorsal surface while the other appears to sink into the 

 substance of the bulb to the median side of the restiform body ; 

 and in a transverse section of the bulb (Fig. 110) just behind the 

 pons the two roots may be seen embracing the restiform body, one 

 passing on its dorsal and the other on its ventral side. The former 

 is called the dorsal root (Fig. 110), or sometimes the lateral root, 

 or since it reaches farther back or lower down than the other, the 

 posterior or inferior root ; the latter is called the ventral root (Fig. 

 Ill), or sometimes the median root, or since it reaches farther 

 forward or higher up than the other, the anterior or superior root. 

 When we come to study the ear we shall find that one division of 

 the auditory nerve is distributed to the cochlea alone and is called 

 the nervus cochlearis, the rest of the nerve being distributed to the 

 utricle, saccule and semicircular canals as the nervus vestibularis. 

 As we shall see, there are reasons for thinking that the vestibular 

 nerve carries up to the brain from the semicircular canals impulses 

 other than those or besides those which give rise to sensations of 

 sound, whereas the cochlear nerve appears to be exclusively con- 



