98 



THE EAR. 



The nerve of Jacobson or tympanic nerve enters the tympanum by a small 

 foramen near its floor, which forms the upper end of a short canal in the petrous 

 portion of the temporal bone, beginning at the base of the skull between the carotid 

 foramen and the jugular fossa. The nerve connecting it with the carotid plexus is 

 above and in front, and passes through the bone directly from the carotid canal. 

 The branch to the great superficial petrosal nerve is lodged in a canal which opens 

 on the inner wall of the tympanum in front of the fenestra ovalis. The small 

 superficial petrosal nerve also leaves at the fore part of the cavity beneath the canal 

 for the tensor tympani. 



The tensor tympani muscle obtains its nerve from the internal pterygoid of the 

 fifth through the otic ganglion ; as already mentioned its nerve is provided with a 

 small ganglion. The stapedius receives filaments from the facial nerve. 



The chorda tympani, arising from the facial near the lower end of the aqueduct 

 of Fallopius, takes a recurrent course to the tympanum, which it enters by an 



Fig. 105. THE FACIAL NERVE IN ITS CANAL, 



WITH ITS CONNECTING BRANCHES, &C. 



(From Sappey, after Hirschfeld and Le- 

 veille.) 2 



The mastoid and a part of the petrous bone 

 have been divided nearly vertically, and the 

 canal of the facial nerve opened in its whole 

 extent from the internal meatus to the stylo- 

 mastoid foramen ; the Vidian canal has also been 

 opened from the outer side : 1, facial nerve in 

 the first horizontal part of its course ; 2, its 

 second part turning backwards ; 3, its vertical 

 portion ; 4, the nerve at its exit from the stylo- 

 mastoid foramen ; 5, geniculate ganglion ; 6, 

 large superficial petrosal nerve ; 7, spheno- 

 palatine ganglion ; 8, small superficial petrosal 

 nerve; 9, chorda tympani ; 10, posterior auricu- 

 lar branch cut short ; 11, branch to the digastric 

 muscle ; 12, branch to the stylo-hyoid muscle ; 

 13, twig uniting with the glosso-pharyngeal nerve (14 and 15). 



aperture in the posterior wall (iter chordce posterius) just below the level of the 

 pyramid. From this place it passes with a slight curve across the cavity near the 

 outer boundary, and crossing successively the posterior part of the membrana 

 tympani, the handle of the malleus near its neck, and the processus gracilis of the 

 same bone, finally enters a small canaljj (iter chordce anterius) in the bone close to 

 the Glaserian fissure (fig. 90, ch). It is invested by the fold of the lining- 

 membrane already mentioned. 



THE INTERNAL EAR, OR LABYRINTH. 



The inner, essential part of the organ of hearing, is contained in the petrous 

 portion of the temporal bone. It consists of a complex cavity the osseous laby- 

 rinth hollowed out of the bone, and containing the membranous labyrinth. 



The osseous labyrinth is incompletely divided into three parts, named the vesti- 

 bule, the semicircular canals, and the cochlea. They are lined throughout by a thin 

 periosteal membrane, within which there is a clear fluid named perilymph, or liquor 

 Cotunnii. 



The membranous labyrinth being distinctly smaller than the bony labyrinth, a 

 space is left between the two, occupied by the perilymph just referred to. The 

 membranous structure is lined throughout by epithelium, and at certain parts 

 receives branches of the auditory nerve. It contains a fluid named the endolymph, 

 and consists of several parts, viz. : the ntricle, saccule, semicircular canals, and 

 membranous cochlea. 



