86 INNERVATION. [CHAP. XVIII. 



sends some filaments into the labyrinth to the blood-vessels, and to 

 the muscular structure of that portion of the ear. 



At the bottom of the meatus, the portio mollis divides into two 

 branches, one to the vestibule and semicircular canals, the other to 

 the cochlea. 



The vestibular nerve divides into three branches : the largest is 

 uppermost, and penetrates the depression which is immediately be- 

 hind the orifice of the aqueduct of Fallopius to be distributed to 

 the utriculus, and to the ampullae of the superior vertical and the 

 horizontal semicircular canal. The second branch of the vestibular 

 nerve is distributed to the sacculus, and the third to the posterior 

 vertical semicircular canal. 



The cochlear nerve penetrates the funnel-shaped depression at the 

 bottom of the auditory canal, and proceeds from it through the 

 numerous foramina, by which its wall is pierced, in a spiral manner, 

 to the lamina spiralis of the cochlea. 



The mode of distribution of these nerves has been already de- 

 scribed. 



The labyrinth receives nerves from no other source but the portio 

 mollis, unless we suppose the portio intermedia to consist of fila- 

 ments from the facial which accompany the ramifications of that 

 nerve into that part of the ear. 



That the portio mollis is the nerve of hearing is abundantly 

 proved by the following arguments: 1. The distribution of the 

 nerve to the internal ear, to which no other nerve of any import- 

 ance is distributed. 2. Its softness of texture and cerebriform 

 character distinguish it from ordinary nerves of sensation or mo- 

 tion. 3. Diseased states of it or of parts immediately near to its 

 origin affect the sense of hearing, whilst a paralytic state of the 

 portio dura or of the fifth does not affect the sense. 



Of the Nervous Apparatus accessory to the Organ of Hearing. 

 Besides the auditory nerve there are others which influence the 

 auditory apparatus. These are branches of the portio dura, 

 branches of the nerve of Jacobson, from the glosso-pharyngeal, and 

 from the otic ganglion. 



These nerves present a striking analogy with those which are 

 distributed to the eye. 



The tympanum receives branches from the facial, and glosso-pha- 

 ryngeal, and probably from the sympathetic. 



The facial in its passage through the aqueduct of Fallopius, gives 

 off the chorda tympani, which, however, seems to have no physiolo- 

 gical connexion with the tympanum or its contents. The stapedius 



ins 



