SENSE OF HEARING. 

 [Fig. 191. 



433 



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 vestibule, 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 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 contained membranous canal ; 5, the 

 ampullaof 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, resulting from the union of the perpendicular with 

 the oblique semicircular canal ; 10, the membranous common canal terminating in the sacculus com- 

 munis ; 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 saccu- 

 lus communis near to the otoconite ; the extremity of the sacculus above the otoconite is lodged in the 

 superior ventricle of the vestibule, and that below it 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; 16, 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 lympani being benealh 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 included within the falciform curve of the extremity 

 of the lamina spiralis is the helicotrema; 20, the infuudibulum.] 



experiment (xii.), that vibrations are transmitted with very much greater in- 

 tensity to water, when a tense membrane, and a chain of insulated solid bodies 

 capable of free movement, are successively the conducting media, than when 

 the media of communication between the vibrating air and the water are the 

 same tense membrane, air, and a second membrane : or, to apply this fact 

 to the organ of hearing, the same vibrations of the air act upon the fluid of the 

 labyrinth with much greater intensity, through the medium of the chain of 

 auditory bones and the fenestra ovalis, than through the medium of the air of 

 the tympanum and the membrane closing the fenestra rotunda. The fenestra 

 rotunda is not to be considered as having any peculiar relation with the cochlea; 

 since, in the Turtle tribe, the former exists without the latter. 



566. In regard to the functions of particular parts of the labyrinth, no cer- 

 tainty can be said to exist. From the experimental results already stated, it 

 appears likely that, the greater the extension of the cavity into the dense sub- 

 stance of the bone, the greater will be the resonance communicated to the 

 fluid, and thence transmitted to the nerves exposed to its influence. It is 

 37 



