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INTERNAL EAR. 99 



are called scalse, that nearest to the apex being the scala 

 vestibuli, and the other the scala tympani; the scala vesti- 

 bnli opens by an oval aperture into the anterior part of the 

 vestibule; the scala tympani is shut off from the vestibule, 

 and terminates at the fenestra rotunda, which is closed by 

 a membrane. Communicating with the scala tympani is 

 the aquaeductus cochleae, which opens on the under surface 

 of the petrous portion of the temporal bone, and transmits 



vein from the cochlea to the internal jugular vein. 



The vestibule, the semicircular canals, and the scalae of 

 he cochlea are lined with a delicate fibro-serons membrane, 

 which secretes a thin fluid called the liquor Cotunnii. 



The MEMBRANOUS LABYRINTH is composed of sacs, over 

 which the auditory nerve is expanded, and which contain a 

 fluid called the liquor Scarpae ; these sacs are two in number, 

 he utricle and the saccule, and are a perfect counterpart, 

 n form, of the vestibule and semicircular canals. The 

 utricle is situated in the posterior and upper part of the 

 vestibule, opposite the fovea semi-elliptica in the roof. 

 The saccule is smaller than the utricle, and is placed in 

 front of the latter, in the hollow of the fovea hemispherica. 

 The membranous tubes for the semicircular canals are pro- 

 longations from the utricle. In these sacs will be found 

 two small calcareous concretions, called otoconites. The 

 membranous labyrinth floats in the liquor Cotunnii. 



The auditory nerve divides into two branches in the 

 meat us auditorius interims, called the cochlear and the ves- 

 tibular. 



The cochlear branch enters by numerous filaments at the 

 base of the modiolus, and these, bending outward, are dis- 

 tributed upon the lamina spiralis. 



The vestibular branch divides into three filaments, one of 

 which goes to the utricle and to the membranous labyrinth 

 in the ampulla of the superior and horizontal canals ; the 

 second to the saccule, and the third to the membrane in 

 the ampulla of the oblique canal. 



The internal ear is supplied by the internal auditory 

 artery, a minute branch of the basilar artery, which enters 

 the internal meatus with the auditory nerve, and divides into 

 two branches, one for the cochlea and one for the vestibule. 



