762 THE XERVOrS SYSTEM 



tyiupaiii, while the posterior part of the organ is supplied directlj'. (See Glosso-piiakvn»;kai- 

 2S ERVE. ) 



At its superficial origin the facial nerve is placed immediately internal to tlx- 

 auditory nerve, the pars intermedia of A\'risl»erg intervening l)etween them. As 

 the facial nerve enters the internal auditory meatus, it is placed above the auditory 

 nerve. It then parts company with the auditory nerve by entering the aqueduct 

 of Fallo})ius. While traversing the aqueduct, it necessarily follows the windings 

 of that canal. It passes at first outwards and forw^ards through the bone above 

 and between the cochlea and the vestibule. It then makes a sharp bend, and runs 

 backwards and slightly downwards, being separated from the tym})anum in this 

 j)art of its course only by a very thin scale of bone and by the mucous membrane 

 lining the cavity. Lastly, it runs directly downwards, and emerges at the stylo- 

 mastoid foramen. The portion of the nerve corresponding to the first bend is 

 c()iisideral)ly thickened, and contains some nerve-cells; it is called tlie geniculate 

 ganglion. The ganglionic substance forms a little conical cap on the bend of tlie 

 nerve, the apex of the cone being directed towards the hiatus Fallo}>ii. 



After its emergence from the stylo-mastoid foramen, the facial nerve runs 

 downw^ards and forwards within the substance of the parotid gland, and terminates 

 by dividing into two divisions — an upper or temporo-facial, and a loAver or cervi(v-»- 

 facial. 



The branches of the facial nerve may be classified into three sets: — (1 ) Branches 

 given off within the aipteduct of Fallopius; (2) branches from the extracranial 

 portion of the nerve before its terminal division; (3) branches of the temporo-facial 

 and cervico-facial divisions. 



(1) Six branches are given off within the aqueduct: viz. three from the genicu- 

 late ganglion, the great, the lesser, and the external superficial petrosal nerves; 

 and three from the facial nerve in the descending part of its course — viz. the nerve 

 to the stapedius, the chorda tympani, and a communicating twig to the pneumo- 

 gastric. 



(a) The great superficial petrosal nerve receives a communicating filament 

 from the tympanic liranch of the glosso-})haryngeal, and leaves the acjUeduct by 

 ])assing through the hiatus Fallopii. It runs f(jrwards and inwards in a groove on 

 the petrous portion of the temporal bone under cover of the dura mater. It passes 

 beneath the Gasserian ganglion, and pierces o))liquely the cartilaginous substance 

 which occupies the foramen lacerum medium; here it is joined by the great deej) 

 petrosal nerve, and forms, with the latter, the Vidian nerve as already described. 



(6) The lesser superficial petrosal nerve arises from the geniculate ganglion 

 external to the preceding. It receives a relatively large communication from the 

 tympanic branch of the glosso-pharyngeal. This conmiunication is often considered 

 to l)e the main root of the nerve (Schw^albe and others). It leaves the a(iueduct 

 through a canal which is placed external to the hiatus Fallopii, and passes forwards 

 for a short distance, lying in a groove in the bone, under cover of the dura mater. 

 It escapes from the cranium through a small foramen situated between the foramen 

 ovale and the foramen spinosum (canalis innominatus), and enters the otic ganglion. 

 Occasionally it leaves the skull by traversing the suture between the great wing of 

 the sphenoid and the petrous portion of the tenq^oral bone, or by passing through 

 the foramen ovale. 



(c) The external superficial petrosal is the smallest of the three petrosal 

 nerves. It passes through a minute canal in the temporal bone immediately external 

 to the point of emergence of the lesser su})erficial nerve. It then runs forwai-ds. 

 under cover of the dura mater, and joins the j^lexus of the sympathetic on the miildle 

 meningeal artery close to the forammi spinosum. 



(rf) The nerve to the stapedius is a minute twig which is given oft' by the 

 facial nerve immediately below the second bend which the nerve forms within the 

 arjueduct. It passes through a small canal leading from the aqueduct to the interior 

 of tlie pyramid, and ends in the muscular sul)stance of the stapedius. 



(g) The chorda tympani arises from the facial nen'e about five millimetres 

 above the stylo-mastoid foramen. It pursues a slightly recui'rent course, iq)wards 

 and forwards, through the iter chorda" posterius. and thus enters the tyni])anum. 



