FACIAL SERVE 



761 



SEVENTH OR FACIAL NERVE 



The seventh (jr facial nerve is formed by two distinct parts — the main trunk, 

 or facial nerve proper, and an accessory ]>ortion, the pars intermedia of \\'risl)er<f. 

 Tlie facial nerve jjroper arises from an elongated nucleus which is deeply j^laced in 

 tlie reticular formation of the pons below the Hoor of the fourth ventricle. This 

 nucleus commences at the level of the striae acustic«, and extends brainwards for 

 al)out four millimetres. The fibres which arise from it ])ursue a remarkal)ly tortuous 

 course within the sul»stance of the ]>ons. At first they i)ass Ijackwards and inwards 

 so as to approach the ependyma of tlie Hoor of the fourth ventricle close to the 

 sulcus longitudinalis niedianus (crus of origin). They then run upwards and for- 

 wards in a compact l)undle ( fasciculus teres, or ascending crus), which produces 

 an elevation (eminentia teres) on the Uoor of the fourth ventricle immediately 

 external to the median fissure. The bundle of fibres then l)ends, and is directed 

 at right angles to its former course; it arches outwards over the nucleus of the 

 sixth nerve, and passes forwards, outwards, and chjwn wards (issuing crus). In 

 this part of its course it passes to the outer side of its own nucleus, l)etween the 

 latter and the ascending root of the fifth nerve. Finally it emerges at the lower 

 l)()rder (jf the pons in the interval between the olivary and restiform liodies f super- 

 ficial origin). 



From the above description, it will Ix' seen that the facial nerve embraces the 



Fi(i. 44s. — Dia(;ramm.\tic Lateral View of the Origin ok the Facial Nkkve. Kmuse. ) 



SUPERIOR OLIVE 

 ASCEXDiyO CEL'S 



yrCLEl.S OF A BDUCEXS 

 CRCS OFORIOIN 



yiCLEIS OF FACIAL 

 MEIU'LLA 



POXS 



OLIVARY NUCLEUS 



nucleus of the abducens; the term genu nervi facialis internus is applierl to the 

 nerve in this part of its course. Within the substance of the i)ons the issuing root 

 t^f the facial nervx' is joined l)y fibres from the oculo-motor and hypoglossal nuclei 

 which pass to it by means of the posterior longitudinal bundle. The fibres from 

 the oculo-motor nucleus are distributed by the temporal ])ranches of the facial 

 nerve to the corrugator supercilii, the upper part of the orbicularis paljiebrarum and 

 to the frontalis muscles, whilst the fibres received from the hy]>oglossal are said to 

 sup])ly the orbicularis oris. 



T\\{' pars intermedia of ^A^risbe^g arises from the extreme upper i ]»roximal) 

 end of the sensory nucleus of the glosso-pharyngeal nerve (Duval). Its fibres 

 ]>ass obli(juely through the substance of the pons, and emerge at the lower border 

 of the last-named structure innnediately external to the facial nerve, between the 

 latter and the auditory nen'e (suj)erficial (jrigin). Thence the nerve ])asses, in the 

 form of a small compact bundle, and enters the internal auditory meatus. In this 

 situation it lies on the upper surface of the auditory nerve, while the facial is 

 placed above it. It joins the facial nerve at the commencement of the geniculate 

 ganglion. 



This nerve is rocardorl as an aberrant fasciculus of the trl()Sso-iihar3'iigcal nerve, an<l aiMi- 

 tional support is siven to this view hy the fact that it also receives fibres from the funiculus 

 solitarius (Testut). The chorda tyui|)ani is usually regarded as the coutiuuatiou of it, and thus 

 the anterior part of the tongue receives fibres from the glosso-pharyugeal through the chorda 



