464 



COCHLEA MODIOLUS. 



Fig. 20G.f 



Fig. 205.* longed to the opposite wall by means of a 



membranous layer, so as to constitute a 

 complete partition, the lamina spiralis. 

 The osseous lamina spiralis consists of two 

 thin lamella? of bone, between which, and 

 through the perforations on their surfaces, 

 the filaments of the cochlear nerve reach 

 the membrane of the cochlea. At the apex 

 of the cochlea the lamina spiralis terminates 

 by a pointed, hook-shaped process, the 

 hamulus laminae spiralis. The tw r o scalae 

 of the cochlea, which are completely sepa- 

 rated throughout their length in the living ear, communicate superiorly, 

 over the hamulus laminae spiralis, by means of an opening common to 

 both, which has been termed by Breschet helico- 

 trema (s'Xif, Xi<r<rw volvere r^a). Inferiorly, 

 one of the two scalae, the scala vestibuli, termi- 

 nates by means of an oval aperture in the ante- 

 rior ventricle of the vestibule ; while the other, 

 the scala tympani, becomes somewhat expand- 

 ed, and opens into the tympanum through the 

 fenestra rotunda (fenestra cochleae). Near the 

 termination of the scala tympani is the small 

 opening of the aquaeductus cochleae. 



The internal surface of the osseous labyrinth 

 is lined by a fibro-serous membrane^ which is 

 analogous to the dura mater in performing the 

 office of a periosteum by its exterior, whilst it 

 fulfils the purpose of a serous membrane by its 

 internal layer, secreting a limpid fluid, the aqua 



* The cochlea divided parallel with its axis, through the centre of the modiolus 

 After Breschet. 1. The modiolus. 2. The infundibulum in which the modiolus termi- 

 nates. 3, 3. The cochlear nerve, sending its filaments through the centre of the modio- 

 lus. 4, 4. The scala tympani of the first turn of the cochlea. 5, 5. The scala vestibuh 

 of the first turn ; the septum between 4 and 5 is the lamina spiralis; a filament of the 

 cochlear nerve is seen passing between the layers of the lamina to be distributed upon 

 the membrane which invests the lamina. 8. Loops formed by the filaments of the 

 cochlear nerve on the lamina spiralis. 9, 9. Scala tympani of the second turn of the 

 cochlea. 10, 10. Scala vestibuli of the second turn; the septum between the two is the 

 lamina spiralis. 11. The remaining half turn of the scala vestibuli; the dome placed 

 over this half turn is the cupola ; a line leads from the numeral to the remaining half 

 turn of the scala tympani. The lamina of bone which forms the floor of the scala ves- 

 tibuli curves spirally round to constitute the infundibulum (2). 14. The helicotrema 

 through which a bristle is passed ; its lower extremity issues from the scala tympani of 

 the middle turn of the cochlea. The hamulus laminae spiralis is seen in front of the 

 bristle. 



j- The labyrinth of the left ear, laid open, in order to show its cavities and the mem- 

 branous labyrinth. After Breschet. 1. The cavity of the vestibule, opened from its 

 anterior aspect in order to show the three-cornered form of its interior, and the mem- 

 branous labyrinth which it contains. The figure rests upon the common saccule of the 

 membranous labyrinth, the sacculus communis. 2. The ampulla of the superior or 

 perpendicular semicircular can&.!, receiving a nervous fasciculus from the superior 

 branch of the vestibular nerve, 3. 4. The superior or perpendicular canal with its 

 contained membranous canal. 5. The ampulla of the inferior or horizontal semicircular 

 canal, receiving a nervous fasciculus from the superior branch of the vestibular nerve. 

 6. The termination of the membranous canal of the horizontal semicircular canal in the 

 wtcculus communis. 7. The ampulla of the middle 07 oblique semicircular canal, 



