610 ANIMAL PHYSIOLOGY. 
When the middle ear is not functionally active, it is stilt 
possible, so long as the auditory nerve is normal, to hear 
vibrations of a body (as a tuning-fork) held against the head; 
though, as would be expected, discrimination as to pitch ‘is 
very imperfect. 
Auditory impulses originate within the inner ear—that is 
to say, in the vestibule and possibly the semicircular canals, 
pa 
mie 
ie 
Fie. 449.—Diagram intended to illustrate the processes of hearing (after Landois). AG,: 
external auditory meatus; 7, tympanic membrane; K, malleus; a, incus; P, middle 
ear: o, fenestra ovalis: r, fenestra rotunda; pl, scala tympani; vt, scala vestibuli ; VY, 
vestibule ; S, saccule ; U, utricle; H, semicircular canals; TH, Eustachian tube. Long 
arrow indicates line of traction of tensor tympani; short curved one that of Stapedius. 
but especially in the cochlea. It is to be remembered that the 
whole of the end-organ concerned in hearing is bathed by endo- 
lymph; and that the vibrations of the latter are originated by 
Fie. 450.—Section through one of the coils of cochlea (after Chauveau). ST, scala tympanl; 
SV, scala vestibuli; CC, cochlear canal (scala media): Co, organ of Corti; R, membrane 
of Reissner ; b, membrana basilaris ; 1s0, lamina spiralis ossea; 1, membrana tectoria; 
1, 2, rods of Corti ; nc, cochlear nerve with its ganglion, gs. 
