THE EAR 



221 



the endolymph, and thence to the otoliths^ hair-like processes, and 

 the terminations of the auditory nerve. This nerve conveys the 

 disturbance to the brain, giving rise to the sensation of hearing. 

 Sound vibrations may also be transmitted to the auditory nerve 

 through the bones of the skull, without penetrating the structures 

 of the ear. 



It is probable that the cochlea enables us to determine the pitch of a note, 

 and also to distinguish between the qualities of different sounds ; while the 

 semicircular canals aid us in distinguishing sounds according to their intensity 

 or loudness, and also in determining the directions from which the sounds 

 proceed. 



SUMMARY. 



r Outer 



Middle 



, Cartilaginous framework. 

 Fatty tissue. 

 J Muscles. 

 1 Skin. 



I Collects sound waves and reflects 

 ^ them into the auditory canal. 

 l\\ inch long. 



J Closed internally by the drum. 

 j Glands secrete ' max. ' 

 I Hairs directed outwards. 

 An irregular cavity in the temporal bone. 

 / Malleus. 

 \ Incus. 

 I Stapes. 



i Fenestra ovalis closed by the stapes. 

 | Fenestra rotunda closed by a mem- 

 V brane. 



Pinna 



Canal 



Bones 



Openings 



, Vestibule | Central portion. 

 I Fenestra ovahs. 



Internal 



Canals 



labyrinth 



\ 



Cochlea 



Path of the Sound Waves . 



\ Three in number. 



t Open into the vestibule. 



(A spiral tube. 

 2\ turns round the modio- 

 "his. 

 Fenestra rotunda. 

 /Within the osseous. 

 I Similar in shape. 



Membranous J Surrounded by perilymph. 

 labyrinth 1 Contains endolymph. 



| Otoliths and hair-like processes. 

 * Terminal fibres of auditory nerve. 



r Pinna. 



Auditory canal. 



Drum. 



Ossicles. 



Perilymph. , 



Endolymph. 



Otoliths and hairs. 



Auditory nerve. 

 * Brain. 



