ANIMAL AND VEGETABLE 229 



ear by being fixed into an oval opening in a bony tubular 

 labyrinth consisting of parts termed the vestibule, the 

 semicircular canals, and the cochlea. Inside the bony 

 labyrinth is a nearly similar labyrinth of membrane filled 

 with liquid, a liquid also lying between the bony and the 

 membranous labyrinth." 



Fig. 123. SCHEME OF THE ORGAN OF HEARING. ( Landois and Stirling.) 

 HG, external auditory meatus ; T, tympanic membrane ; malleus 

 with its head, short process (kf), and handle (m) ; a, incus with its 

 short process (x) and long process the latter is united to the stapes (s) 

 by means of the Sylvian ossicle (z) ; P, middle ear ; o, fenestra ovalis ; 

 r, fenestra rotunda ; x, beginning of the lamina spiralis of the cochlea ; 

 pt, its scala tympani, and vt, its scala vestibuli ; V, vestibule ; S, saccule ; 

 U, utricle ; H, semicircular canals ; TE, Eustachian tube. The long 

 arrow indicates the line of traction of the tensor tympani ; the short 

 curved one, that of the stapedius. 



These liquids are known as endolymph and perilymph 

 respectively, and according to Landois and Stirling the 

 end-organs of the acoustic nerve lie in the endolymph and 

 on membranous expansions of the cochlea and semi- 

 circular canals. 



" The vibrations conveyed to this fluid by the move- 

 ment of the base of the stapes excite the peculiar epithelium 

 of the inner surface of the membranous labyrinth, on and 

 in which are distributed the auditory nerve-filaments. 

 Impulses pass from these filaments along the nerve lying 

 in the internal meatus to the brain, and there produce that 



