ANATOMY OF THE INTERNAL EAK. 219 



auditory nerves enter the internal auditory meatus, they di- 

 vide into an anterior, or cochlear, and a posterior, or vestib- 

 ular branch. The vestibular branch divides into three smaller 

 branches, a superior and anterior, a middle, and a posterior 

 branch. The superior and anterior branch, the largest of the 

 three, is distributed to the utricle, the superior semicircular ca- 

 nal, and the external semicircular canal. The middle branch 

 is distributed to the saccule. The posterior branch passes to 

 the posterior semicircular canal. The nerves distributed to 

 the utricle and saccule penetrate at the points occupied by 

 the otoliths, and the nerves going to the semicircular canals 

 pass to the ampullae, which also contain otoliths. In each 

 ampulla, at the point where the nerve enters, is a transverse 

 fold, projecting into the canal and occupying about one-third 

 of its circumference, called the septum transversum. 



The nerves terminate in essentially the same way in the 

 sacs of the vestibule and the ampullae of the semicircular ca- 

 nals. At the points where the nerves enter, in addition to 

 the otoliths, are cells of cylindrical epithelium, of various 

 forms, which pass gradually into the general pavement-epi- 

 thelium of the cavities. In addition to these cells, are fusi- 

 form, nucleated bodies, the free ends of which are provided 

 with hair-like processes, called fila acustica. These are about 

 g-J-o- of an inch in length, and are distributed in quite a regu- 

 lar manner around the otoliths. The nerves form an anasto- 

 mosing plexus beneath the epithelium, and probably termi- 

 nate in the fusiform bodies just described as presenting the 

 fila acustica at their free extremities. In the sacs of the ves- 

 tibule and in the semicircular canals, nerves exist only in the 

 macula acustica and the ampullae. 



The cochlear division of the auditory nerve breaks up into 

 numerous small branches, which pass through foramina at the 

 base of the cochlea, in what is called the tractus spiralis f ora- 

 minulentus. These follow the axis of the cochlea and pass, in 

 their course toward the apex, between the plates of the bony 

 spiral lamina. Between these plates of bone, the dark-bor- 



