460 MEMBRANOUS LABYRINTH. 



of a communication originally subsisting between the dura mater 



and the cavity of the labyrinth.* 



The MEMBRANOUS LABYRINTH is smaller in size, but a perfect 

 counterpart, with respect to form, of the 

 vestibule and semicircular canals. It 

 consists of a small elongated sac, sacculus 

 communis (utriculus communis) ; of three 

 semicircular membranous canals, which 

 correspond with the osseous canals, and 

 communicate with the sacculus com- 

 munis ; and of a small round sac (saccu- 

 lus proprius), which occupies the anterior 

 ventricle of the vestibule, and lies in close 

 contact with the external surface of the 

 sacculus communis. 



The membranous semicircular canals 

 are two-thirds smaller in diameter than 

 the osseous canals. The membranous 

 labyrinth is retained in its position by 



* Cotunnius regarded these processes as tubular canals, through which the supera- 

 bundant aqua labyrinth! might be expelled into the cavity of the cranium. Mr. Whar- 

 ton Jones, in the article " Organ of Hearing" in the Cyclopaedia of Anatomy and 

 Physiology, also describes them as tubular canals which terminate beneath the dura 

 mater of the petrous bone in a small dilated pouch. In the ear of a man deaf and 

 dumb from birth, he found the termination of the aqueduct of the vestibule of unusu- 

 ally large size in consequence of irregular developement. 



t 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 canal, receiving a nervous fasciculus from the superior 

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

 tained 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 sacculus communis. 7. The ampulla of the middle or oblique semicircular canal, 

 receiving a nervous fasciculus from the inferior branch of the vestibular nerve. 8. The 

 oblique semicircular canal with its membranous canal. 9. The common canal, result- 

 ing from the union of the perpendicular with the oblique semicircular canal. 10. The 

 membranous common canal terminating in the sacculus communis. 11. The otoconite 

 of the sacculus communis seen through the membranous parietes of that sac. A nervous 

 fasciculus from the inferior branch of the vestibular nerve is seen to be distributed to 

 the sacculus commnnis near to the otoconite. The extremity of the sacculus above 

 the otoconite is lodged in the superior ventricle of the vestibule, and that below in the 

 inferior ventricle. 12. The sacculus proprius situated in the anterior ventricle; its 

 otoconite is seen through its membranous parietes, and a nervous fasciculus derived 

 from the middle branch of the vestibular nerve is distributed to it. The spaces around 

 the membranous labyrinth are occupied by the aqua labyrinthi. 13. The first turn of 

 the cochlea; the figure is situated in the scala tympani. 14. The extremity of the 

 scala tympani corresponding with the fenestra rotunda. 15. The lamina spiralis; the 

 figure is situated in the scala vestibuli. 1 G. The opening of the scala vestibuli into the 

 vestibule. 17. The second turn of the cochlea ; the figure is placed upon the lamina 

 spiralis, and therefore in the scala vestibuli, the scala tympani being beneath the lamina. 



18. The remaining half turn of the cochlea; the figure is placed in the scala tympani. 



19. The lamina spiralis terminating in a falciform extremity. The dark space in- 

 cluded within the falciform curve of the extremity of the lamina spiralis is the heli- 

 cotrema. 20. The infundibulum. . 



