458 COCHLEA MODIOLUS. 



superior), is directed transversely across the petrous portion of the 

 temporal bone, forming a projection upon the anterior face of the 

 petrous bone. It commences by means of an ampulla in the superior 

 ventricle of the vestibule, and terminates posteriorly by joining with 

 the oblique, and forming a common canal, which opens into the 

 upper part of the posterior ventricle. The middle or oblique canal 

 (canalis semicircularis verticalis posterior), corresponds with the 

 posterior part of the petrous portion of the temporal bone ; it com- 

 mences by an ampullary dilatation in the posterior ventricle, and 

 curves nearly perpendicularly upwards to terminate in the common 

 canal. In the ampulla of this canal are numerous minute openings 

 for nervous filaments. The inferior or horizontal canal (canalis 

 semicircularis horizontalis), is directed outwards towards the base 

 of the petrous bone, and is shorter than the two preceding. It 

 commences by an ampullary dilatation in the superior ventricle, and 

 terminates in the posterior ventricle. 



The COCHLEA (snail shell), forms the anterior portion of the laby- 

 rinth, corresponding by its apex with 

 Fig. 140.* the anterior wall of the petrous bone, 



and by its base with the anterior 

 depression at the bottom of the cul 

 de sac of the meatus auditorius in- 

 ternus. It consists of an osseous 

 and gradually tapering canal, about 

 one inch arid a half in length, which 

 makes two turns and a half spirally 

 around a central axis called the 

 modiolus. 



The central axis or modiolus is 

 large near its base where it corre- 

 sponds with the first turn of the cochlea, and diminishes in diameter 

 towards its extremity. At its base it is pierced by numerous 

 minute openings which transmit the filaments of the cochlear nerve. 

 These openings are disposed in a spiral manner, hence they have 

 received from Cotunniusf the name of tractus spiralis foraminu- 



* 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 ter- 

 minates. 3, 3. The cochlear nerve, sending its filaments through the centre of the 

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

 vestibuli of the first turn. 6. Section of the lamina spiralis, its zonula ossea ; one of 

 the filaments of the cochlear nerve is seen passing between the two layers of the lamina 

 spiralis to be distributed upon the membrane which invests the lamina. 7. The mem- 

 branous portion of the lamina spiralis. 8. Loops formed by the filaments of the 

 cochlear nerve. 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 scala tympani of the remaining half turn. 12. The remaining half turn of the 

 scala vestibuli ; the dome placed over this half turn is the cupola. 13. The lamina of 

 bone which forms the floor of the scala vestibuli curving 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. 



t Dominico Cotunnius, an Italian physician; his dissertation " De Aquceductibus 

 Auris Humanae Interne," was published in Naples in 1761. 



