004 THE BRAIN. 



(Fig. 131, (7.), a series of roots ; of these the lowest, the accessory roots, spring 

 from the hind part, the highest, the glosso-pharyngeal roots, from the front 

 part (and it is these especially which pierce the gelatinous substance Fig. 

 133, IX. a), and the intermediate, the vagus roots, from the middle part of 

 the combined nucleus. Hence we may speak of the hind part of the whole 

 nucleus as being the accessory nucleus, the middle part as the vagus nucleus, 

 and the front part as the glosso-pharyngeal nucleus. 



All the fibres, however, of the roots of these three nerves do not take 

 origin from the nucleus in question ; some of the fibres start in a different 

 way. In sections of the bulb above the decussation of the pyramid a 

 patch of gray matter is seen lying in the lateral part of the reticular 

 formation (Fig. 132, X. m.), about midway between ventral and dorsal sur- 

 faces. What is thus disclosed by sections is a column of gray matter, the 

 "nucleus ambiguus" (Fig. 138, wa.), stretching about as far forward and 

 backward as the combined accessory-vago-glosso-pharyngeal nucleus, but 

 placed distinctly more ventrally and somewhat more laterally. (In Fig. 

 138, it and the combined nucleus are represented on different sides of 

 the diagram to avoid confusion through the overlapping of the shad- 

 ing.) From it fibres curve round (Fig. 132, X. m.) to join the accessory- 

 vago-glosso-pharyngeal roots, but especially the vagus roots. It may, 

 therefore, be considered as a second nucleus of the vagus (and possibly 

 of the other) roots. 



But there is yet a third source of some of the fibres of the nerves of which 

 we are speaking. In sections through the bulb there may be seen just ven- 

 tral to and a little lateral to the combined nucleus (Fig. 132, 4, 5, 6, IX. a.) 

 the circular section of a longitudinal bundle of fibres. In the hinder sections 

 (Fig. 132, 4) the bundle is a very thin one, and still further back it is lost to 

 view, though there are reasons for thinking that some of the fibres are con- 

 tinued back into the cervical cord, as far as the origin of the fourth cervical 

 nerve or even beyond ; in the more forward sections (Fig. 132, 5 and 6) it 

 increases in diameter and may be traced forward to the front end of the com- 

 bined nucleus into which it merges. It is a bundle of fibres which, starting 

 successively in the lateral gray matter of the cervical cord and higher up in 

 the reticular formation of the bulb, run longitudinally forward ; the bundle 

 at first increases in size by the addition of fresh fibres at each step ; but fur- 

 ther forward the fibres leave the bundle to pass into the roots of the nerves 

 of which we are speaking, especially of the glosso-pharyngeal, and the bundle 

 eventually ends in front by passing into the glosso-pharyngeal roots. The 

 gray matter from which these fibres take origin does not form a defined com- 

 pact 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 gray matter along a consider- 

 able length. The fibres are, nevertheless, fibres of nerve-roots, and the bundle 

 is called the ascending root of the glosso-pharyngeal, the term ascending being 

 used since it is customary to trace such structures from below upward, that 

 is, from behind forward ; though since the fibres in question are probably 

 afferent fibres carrying impulses backward from the nerves to the gray 

 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 ( 304), it has been spoken of as the respiratory 

 bundle. 



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

 and the glosso-pharyngeal 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 



