554 



ORGAN OF HEARING. 



Nerves of the accessory parts of the apparatus 

 of hearing. 



Nerves of the tympanum. The tympanum 

 receives nerves from different sources from 

 the fifth, the seventh, eighth, and ninth pairs of 

 cerebral nerves. Moreover, its nerves have 

 communication with the sympathetic system. 



The facial nerve or portio dura of the seventh 

 pair rises from the brain by two roots, which 

 unite together in the meatus auditorius inter- 

 nus, but before uniting, the smaller root sends 

 of}' a delicate filament, which forms a commu- 

 nication, as has been mentioned, with the au- 

 ditory nerve. This communication, first pointed 

 out by Swan, has recently been very fully in- 

 vestigated by Arnold. According to the latter, 

 in the middle or at the bottom of the internal 

 auditory meatus, one or several delicate fila- 

 ments go off from the smaller branch of the 

 facial, and join the auditory nerve. After this 

 the facial nerve enters the aqueduct of Fallo- 

 pius, and issues from the cranium through the 

 stylo-mastoid hole. In this course it receives, 

 at the place where it forms the knee-like bend 

 into the aqueduct of Fallopius, the superior 

 branch of the Vidian or superficial petrosal 

 nerve, nervus petrosus superjicialis, s. major. 



The superficial petrosal nerve conies off, 

 along with the inferior branch of the Vidian or 

 deep petrosal nerve, from the posterior part of 

 the spheno-palatine ganglion or ganglion of 

 Meckel. Leaving the deep petrosal nerve at 

 the posterior orifice of the Vidian canal, the 

 superficial petrosal proceeds upwards through 

 the cartilaginous substance in the foramen lace- 

 rum medium, and then runs backwards in the 

 groove on the anterior surface of the petrous 

 bone leading to the hiatus of Fallopius. 

 Having entered the latter, it joins the facial 

 nerve, and forms, with its external fasciculi, a 

 gangliform swelling, intumescentia ganglifor- 

 mis nervij'acialis, of a grayish appearance and 

 soft consistence. 



From this swelling a filament arises by one 

 or two roots, and runs backwards into the in- 

 ternal auditory passage to join the upper por- 

 tion of the auditory nerve, where the first fila- 

 ment joined, and forms with it a small reddish 

 ray elevation, known to and delineated by 

 carpa. 



Another branch, which arises from the gan- 

 glionic swelling, is the chorda tympani. The 

 chorda tympani thus in reality derives its origin 

 both from the facial and the superficial petrosal 

 nerves. The chorda tympani accompanies the 

 facial nerve along the aqueduct of Fallopius 

 till within a little of the exit of the latter by the 

 stylo-mastoid hole. The chorda tympani then 

 leaves the facial nerve at an acute angle, and 

 proceeds upwards in a proper canal in the 

 bone, enters the cavity of the tympanum by the 

 opening just within the posterior part of the 

 groove for the membrana tympani already de- 

 scribed. From this opening it proceeds for- 

 wards between the long process of the incus 

 and the handle of the malleus, to the fissure of 

 Glasser, through the canal beside which, already 

 described, it makes its exit from the cavity of 

 the tympanum. It then descends by the inner 



side of the ascending ramus of the lower jaw, 

 and joins at an acute angle the lingual nerve. 

 In its passage across the cavity of the tympa- 

 num, the chorda tympani anastomoses by one 

 or several filaments with the nerve which the 

 fifth pair sends to the membrana tympani. 



Fig. 259. 



The membrana tympani from within, and tJie course 

 of the chorda tympani across the tympanum, together 

 with the connexions of the malleus and incus (magni- 

 fied). (From Soemmerring ). 



a. Membrana tympani ; b. handle of the malleus 

 and tendon of the internus mallei cut near its in- 

 sertion ; c, c. the chorda tympani. 



To return to the facial nerve. It gives off, 

 a little below the pyramid, a branch to the sta- 

 pedius muscle. 



The pneumogastric nerve, in its passage 

 through the base of the skull, forms a small 

 ganglion, from which springs a nerve which 

 goes to the ear, ramus auricular is nervi vagi. 

 This nerve is joined by a filament from the 

 petrous ganglion of the glosso-pharyngeal ; it 

 then runs, according to Arnold, in a groove in 

 the jugular fossa, and at last arrives at the 

 aqueduct of Fallopius. Here it divides into 

 three branches, the smallest of which runs up- 

 wards in the aqueduct of Fallopius towards 

 the origin of the facial nerve, and unites with 

 it; the second branch, which is somewhat 

 larger, runs downwards, and also anastomoses 

 with the facial. The third and most considera- 

 ble branch will be noticed along with the 

 nerves of the auricle and auditory passage. 



The nervous anastomosis in the tympanum. 

 The principal nerve of this anastomosis is the 

 nerve of Jacobson, or tympanic nerve of Arnold. 



The tympanic nerve, nervus tympanicus, ex- 

 tends between the petrous ganglion of the glosso- 

 pharyngeal nerve and the otic ganglion or gan- 

 glion of Arnold. To follow it from the glosso- 

 pharyngeal, we find it arises from the upper 

 part of the petrous ganglion, along with another 

 filament, which goes to communicate with the 

 ganglion cervicale supremum, and also with the 

 pneumogastric. The tympanic nerve enters, 

 by the tympanic canal already described, the 

 cavity of the tympanum. Here the nerve ap- 

 pears near the anterior margin of the fenestra 

 rotunda, traverses the groove on the promon- 

 tory, arrives in front of the vestibular fenestra, 

 then enters the proper osseous canal, into which 

 the groove on the promontory is continued su- 



