MEMBRANOUS LABYRINTH. 



517 



originally subsisting between 

 the dura mater and the cavity 

 of the labyrinth.! 



The MEMBRANOUS LABY- 

 RINTH is smaller in size, but 

 a perfect counterpart with re- 

 spect to form, of the vestibule 

 and semicircular canals. It 

 consists of a small elongated 

 sac, sacculus communis (utri- 

 culus communis) ; of three semi- 

 circular membranous canals, 

 which correspond with the osse- 

 ous canals, and communicate 

 with the sacculus communis ; 

 and of a small round sac (sac- 

 culus proprius), which occupies 

 the anterior ventricle of the 

 vestibule, and lies in close con- 

 tact with the external surface of 

 the sacculus communis. The 



Fig. 158.* 



* The labyrinth of the left ear, laid open in order to show its cavities 

 and the membranous labyrinth. After Breschet. 1. The cavity of the ves- 

 tibule, opened from its anterior aspect in order to show the three-cornered 

 form of its interior, and the membranous labyrinth which it contains. The 

 figure rests upon the common saccule of the membranous labyrinth, the sac- 

 culus communis. 2. The ampulla of the superior or perpendicular semicir- 

 cular canal, 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 semicir- 

 cular canal, receiving a nervous fasciculus from the superior branch of the ves- 

 tibular 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. Q. The common canal, resulting 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 communis near the otoconite. The extre- 

 mity of the sacculus above the otoconite is lodged in the superior ventricle of 



t Cotunnius regarded these processes as tubular canals, through which the 

 superabundant aqua labyrinthi might be expelled into the cavity of the cra- 

 nium. Mr. Wharton Jones, in the article " Organ of Hearing," in the 

 Cyclopsedia 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 termina- 

 tion of the aqueduct of the vestibule of unusually large size in consequence of 

 irregular development. 



