646 



SEVENTH PAIR OF NERVES. 



guished, from its lesser size, as the " small 

 petrosal nerve" From the hiatus it is con- 

 tinued forwards and slightly inwards for about 

 half an inch, running along the same surface 

 of the temporal bone, but placed a little ex- 

 ternal to the preceding nerve. Arriving at 

 the greater wing of the sphenoid, it perforates 

 the bone by an oblique and minute orifice, 

 which is situated between the foramen rotun- 

 dum and ovale : and appearing on the inferior 

 surface of the base of the skull, it immediately 

 unites with the otic ganglion which lies on the 

 inner surface of the third division of the fifth. 

 During the latter part of this course it is ac- 

 companied by a filament from Jacobson's 

 nerve of the glosso-pharyngeal. This branch, 

 however, leaves the tympanum by a special 

 canal, and is next placed externally to the 

 lesser petrosal nerve on the petrous bone ; but, 

 finally, it joins or runs with it to enter the 

 same ganglion. 



A branch to the membrane which closes 

 the fenestra ovalis is sometimes described as 

 coming from the facial, where it passes, in the 

 aqueduct, above this orifice. 



The minute filament to the stapedius muscle 

 is the next branch of this nerve. It leaves 

 the portio dura and aquasductus Fallopii at 

 about the middle of their second or vertical 

 curve, or nearly on a level with the base of 

 the promontory ; it next enters a small canal 

 in this prominence, which conducts it to the 

 proper osseous cavity for the muscle : it 

 then breaks up and is lost in its substance. 



The chorda tympani, the next connection of 

 the portio dura, is a much larger nerve than 

 any of the preceding branches; it leaves the 

 trunk of the facial at a distance of about the 

 third of an inch from the stylo-mastoid fora- 

 men. Tracing the portio dura in the upward 

 direction, it is first seen to experience a slight 

 thickening, and gradually, by the increasing 

 laxity of the connecting areolar tissue, a to- 

 lerably large branch seems to extricate itself 

 from the trunk at a very acute angle. Di- 

 verging still more, it now altogether quits the 

 aquaeductus Fallopii, and enters a short canal 

 which is appropriated to it, and which is 

 placed anteriorly and externally to the former 

 cavity, occupying the base of the promontory. 

 While yet at a considerable distance from the 

 apex of this eminence, the nerve emerges from 

 its canal by an orifice very near the osseous 

 ring to which the tympanic membrane is fixed. 

 It now crosses the tympanum from its an- 

 terior to its posterior part, and lying close to 

 its outer wall, but covered by a reflection of 

 its mucous membrane, and ascending as it 

 goes, it passes between and at right angles to 

 the long process of the incus and the handle 

 of the malleus, to reach the processus gracilis 

 of the latter bone ; along this process it con- 

 tinues during the remainder of its course in 

 the tympanum. It next leaves the anterior 

 wall of this cavity, and occupies a minute 

 canal in the petrous portion of the temporal 

 bone ; but it is still in close proximity to this 

 process of the malleus, being only separated 

 by a small interval of bone from the Glasserian 



fissure which contains it. It is next seen ex- 

 ternal to the cranium, after coming through 

 the aperture of this canal anteriorly and in- 

 ternally to the fissure. In the remainder of 

 its course it lies deeply in the pterygoid fossa 

 beneath the ramus of the inferior maxilla, and 

 is directed for about an inch downwards, for- 

 wards, and inwards, beneath the spinous 

 process of the sphenoid, and the internal la- 

 teral ligament of the lower jaw attached to it, 

 to join, at an acute angle, the outer side of the 

 gustatory branch from the third division of 

 the fifth. 



Very near the termination of the aqueduct 

 of Fallopius, a minute twig connects the facial 

 and vagus nerves. Following it from this 

 cavity, it is seen to enter a small pore on its 

 anterior surface, which conducts it by a short 

 canal to the under surface of the petrous bone, 

 where it emerges a very short distance in 

 front of the stylo-mastoid foramen, and be- 

 tween it and the jugular fossa. The nervous 

 filament now turns inwards and forwards in 

 front of the jugular vein, and terminates by 

 connecting itself with the pneumogastric, just 

 below its ganglion in the dura mater of the 

 foramen lacerum posticus. 



Besides these branches of the facial within 

 the aqueduct, it appears pretty constantly to 

 give off, while yet contained in this canal, a 

 filament which passes inwards behind the 

 jugular vein, and joins with the glosso-pharyn- 

 geal just below the ganglion of Andersch. 

 Longet states that this branch, after its 

 junction with the glosso-pharyngeal, may ge- 

 nerally be traced to the digastric or stylo-hyoid 

 muscle, in which it often unites for the first 

 time with this nerve by a kind of plexiform 

 arrangement. 



External to the cranium. On leaving the 

 Fallopian canal, the facial nerve immediately 

 enters that portion of the parotid gland which 

 dips downwards behind the styloid process to 

 reach the structures lying deeply at the base of 

 the skull. The nerve next continues through 

 the substance of the gland, being directed for- 

 wards and inwards to about its middle, where 

 it divides into its temporo-facial and cervico- 

 facial portions, the ramifications of which 

 cover the whole side of the face, with part of 

 the neck below and the head above. In its 

 short course previously to this bifurcation, it 

 gives off three branches, the posterior auri- 

 cular, the digastric, and the stylo-hyoid nerves. 



The posterior auricular, the first branch of 

 the facial without the skull, passes upwards 

 from the trunk of the nerve, and turns round 

 the front of the mastoid process, lying at first 

 rather deeply in a depression between the au- 

 ricle of the ear and this prominence, and being 

 enveloped in a dense cellular tissue. Having 

 gained the side of the head, it divides into 

 two branches ; one of these continues back- 

 wards in the horizontal direction, above the 

 insertion of the sterno-mastoid, and crossed by 

 the lesser occipital nerve of the cervical plexus, 

 to reach the posterior belly of the occipito- 

 frontalis muscle, which it supplies : in this 

 course it is covered by a dense fascia, and is 



