M;I;\ \ 727 



a- its properties, because, notwithstanding those anastomoses, its proper 

 fibres preserve their complete iudepeud< 



8. Eighth Pair, or Auditory Nerces. (Tigs. 324, 338.) 



This is the nerve of hearing, and affects a very simple disposition, which 

 we will sum up in a few words. 



Origin. Tht auditory nerve (jwtio mUix) proceeds from the medulla 

 olilongata by two roots, an anterior or lateral, and a posterior. The latter 

 ( 1'iu'. 323, 20) commences on the floor of the fourth ventricle by some 

 convergent strite (linece transcersce, strive medullares), as is admitted in the 

 majority of treatises on human anatomy, though wo have never been able to 

 il ir! -over these stria- in the domesticated animals ; it is afterwards directed 

 outwards in winding round the posterior cerebellar peduncle, and unites with 

 the anterior root on the side of the medulla oblongata. The latter root 

 (Fig. 338, #), consists of a single fasciculus joined with that of the facial, 

 and escapes from between the fibres of the corpus rcstifonno. The nucleus 

 of the auditory nerve has been discovered by Schroader Van der Kolk, a 

 little below that of the facial nerve. 



Course and Ti-rmination. These two roots immediately unite into a 

 single soft cord situated behind that of the seventh pair, with which it is 

 directed outwards to reach the internal auditory hiatus (or meatus.) There 

 it divides into two branches an anterior and posterior, whose fasciculi 

 traverse the foramina at the bottom of that hiatus : the former to gain the 

 axis of the cochlea (the cochlear branch), and the latter the semicircular 

 canals (vcstibular branch.) The description of these two branches will bo 

 deterred till we come to the sense of hearing. 



9. Ninth Pair, or Glosso-Pharyiigeal Nerves. (Figs. 338, 3; 342, 10.) 



The glnsso-pharyngeal is a mixed nerve, which carries general sensation, 

 with gustative sensibility, into the posterior third of the tongue, and excites 

 t ontraction of the pharyugeal muscles. 



Ori'jin. This nerve originates on the side of the medulla oblongata, 

 Ixjhind tho eighth pair, by eight or ten fine roots, some of which arc 

 implanted in the corpus restiformo, while the others, the smallest number, 

 ;><-, !:!< the filaments of the facial nerve, from tho interstice l>ctw-n 

 that body and the lateral column of the medulla oblongata. 1 These roots 

 soon unite in a single cord, \\hich issues from the cranium by ft particular 

 orifice in tlir po.vt'-rior foramen lacerum, and at this {nn'nt exhibits a grey 

 oval-sha{>cd enlargement the ;/<(//;//'"" jn-ti-i>xniii or ynmjlimi of Anderscli, in 

 \\liidi it is somewhat difficult to distinguish tin- motor filaments of tin- 

 nerve from those which arise l>etu. < n the lateral and superior columns of tin- 

 medulla oblongata (Fig. 338, 2). 



>> awl Termination. Scarcely has the glosso-pharyngeal nerve 



: ed from the cranium, IK- fore it descends, in describing a curve whoso 



concavity looks forward, behind the large branch of the OB hyoides, included 



at first between a fold of tho guttural pouch, then between the latter and 



' This disposition, which is raftdfly exposed in the Hone, appeari t.> u- .-uflic-icnt to 



ri-iuov. nil Ilir iloul.i> existing in tin- mimla of a lar-ji- niimK r of nii:it'>ini.-t.-, as t" tin- 

 nature "f tin- glOMO-pharrnge*] nerve. It < \ .ilnitly paMMM* at its origin, n- ni'.t..r 

 lihiiuents, those n fining from the .-aim- \< irt ;i.> tli.- I'.K ial m r\. . ami :IH * iihiii\- lihinu-iit.-* 

 ih. .- fn.ni tin: nn|.us n-HtiforiiM'. li. .-i.li .-,. \vr may ol-jn-t to the flfbta wttah WOOld 



:ittriliuto. tin- motor prujH-rty of tin- gUMO-pMUmifM] in-rv.- to tin- n: 

 liiaiH-licx i.as.-iim Id-tw- tn it nini tin- .-*. \tnili pair, mi tin- ground tliat tin.-- aim.>'< 

 : ir from being con.-tant. ami that in L' in. .-] -re always totally ali--ni. 



