SEVENTH PAIR OF NERVES. 



545 



of the nerve from the aqueduct of Fallopius. 

 The third is extra-cranial, and includes its 

 distribution on the exterior of the skull be- 

 yond this aperture. 



In the cranium, the course of the facial nerve 

 is comparatively short. From the restiform 

 body it passes forwards, lying immediately be- 

 neath and in contact with the pons varolii, 

 and taking the same direction as the portio 

 mollis, which is external and posterior to it. 

 It next enters the meatus auditorius internus 

 in company with this nerve; and finally 

 leaves it by passing through the aperture at 

 the upper part of the termination of this 

 canal, and entering the aqueduct of Fallopius. 



Portio intermedia. With this part of the 

 auditory and facial nerves a third portion is 

 visibly associated ; which is, in all probability, 

 essentially distinct from both. Wrisberg first 

 announced the existence of this nerve as a 

 separate branch ; and from its occupying a 

 position between the " portio mollis " and 

 "portio dura" of the seventh, he named it 

 the " portio media " or " intermedia." It 

 arises by two or three filaments from the 

 restiform body, in the same locality as the 

 neighbouring facial nerve, from which its 

 deeper origin can scarcely be separated. Fo- 

 ville, however, describes its ultimate visible 

 fibres as traceable to a situation which is in- 

 termediate between that of the facial on the 

 one hand, and that of the auditory on the 

 other. He thus considers these three nerves, 

 the facial, intermediate, and auditory, as aris- 

 ing respectively from the anterior pyramid, the 

 olivary column, and the restiform body ; or 

 to use his own language, from the anterior, 

 the lateral, and the posterior tracts of the me- 

 dulla oblongata. Morganti's view of its origin 

 closely approximates to this; but he places it 

 more in connection with the vestibular nerve, 

 and hence more externally. But whatever 

 may be the differences of opinion as to its 

 exact mode of commencement, it is tolerably 

 agreed that it is in very close proximity to 

 the facial nerve, so much so as at first hardly 

 to be separable from it ; and that, at a further 

 stage of its course, it is attached to the vesti- 

 bular branch of the auditory nerve. Con- 

 cerning its behaviour subsequently to this 

 point, anatomists are less unanimous. Thus, 

 some imagine that it continues engaged in the 

 auditory nerve, and accompanies it into the 

 internal ear. Others regard it as returning 

 to the facial nerve, and passing with it into the 

 aqueduct of Fallopius. It is, however, suffi- 

 ciently evident, that the only correct foundation 

 of any of these views must be anatomical ; and 

 since this method of investigation requires not 

 only the artificial unravelling of the trunks, 

 but also necessitates a frequent reference to 

 portions and branches of the facial, as yet un- 

 described, its consideration is deferred until 

 these shall have received some notice. 



In the temporal bone. The facial nerve, 

 entering the aquaeductus Fallopii from the 

 internal auditory meatus, passes, for a very 

 short distance, in a direction forwards, out- 

 wards, and slightly upwards, until it reaches 



VOL. IV. 



the margin of the hiatus Fallopii on the 

 upper surface of the petrous bone : it then 

 suddenly bends backwards upon itself in the 

 horizontal plane. Its next curve differs from 

 the preceding both in character and direction, 

 being much more gradually effected, and occu- 

 pying a vertical plane. The termination of 

 this bend reaches the perpendicular, and 

 opens by the stylo-mastoid foramen on the 

 under surface of the petrous bone, or between 

 the styloid and mastoid processes. In the 

 middle of this course the osseous tube of the 

 aqnasductus Fallopii projects into the cavity 

 of the tympanum ; and the nerve thus passes 

 successively along its roof, above the fenestra 

 ovalis, and then behind the pyramid on the 

 inner side of the cavity ; and, finally, down 

 its posterior surface. 



At the anterior of the acute angle formed 

 by the first bend of the facial nerve in the 

 aqueduct of Fallopius, it experiences a slight 

 enlargement, which has been called, from "its 

 position and shape, the " intumescentia genu- 

 formis." A dense and strong neurilemma 

 here ensheaths the nerve, being a prolongation 

 of dura mater, which is sent inwards on a 

 minute vessel from the middle meningeal 

 artery to enter the canal at the hiatus Fal- 

 lopii. The swelling itself is of a greyish-red 

 colour, but it is somewhat obscured by this 

 thick covering of fibrous tissue. Its nature 

 will be spoken of hereafter. 



Just at this point, the superficial petrosal 

 nerve is connected with the facial. Tracing 

 it forwards from the intumescence, it is seen 

 to pass at once through the neighbouring 

 hiatus Fallopii, and thus it immediately gains 

 the interior of the skull. Within the cranium 

 it passes forwards, downwards, and inwards, 

 lying in a groove on the outer or anterior 

 surface of the petrous bone, and situated be- 

 neath the Gasserian ganglion of the fifth nerve. 

 According to some anatomists, it occasionally 

 passes amongst or through the meshes of the 

 gangliform structure. Still beneath and in- 

 ternal to the ganglion, it is next placed im- 

 mediately external to the internal carotid 

 artery, where this vessel, emerging from the 

 canal of the same name in the temporal bone, 

 springs vertically upwards to form the com- 

 mencement of the posterior limb of the sig- 

 moid turn on the side of the sphenoid. It 

 thus enters the foramen lacerum basis cranii, 

 perforating the cartilaginous substance which 

 closes this bony orifice ; and in this manner 

 it gains the posterior extremity of the vidian 

 canal, which opens into the anterior aspect of 

 this irregular opening. Finally, it continues 

 along this canal to its anterior termination ; and 

 is then prolonged horizontally forwards for a 

 short distance to join Meckel's ganglion, which 

 occupies this part of the spheno-palatine fossa. 



Another nerve comes off from the same 

 knee-shaped bend of the portio dura ; and as 

 it appears from the same horizontal slit, or 

 hiatus Fallopii, whence the preceding emerged, 

 and occupies a very similar position with re- 

 spect to the temporal bone, it has also been 

 named " superficial petrosal," but is distin- 



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