EAR 



1899 



EAR 



ten-cent piece. It is placed obliquely across 

 the auditory canal, and consists of fine, fibrous 

 tissue covered on the outer surface with a 

 thin layer of modified skin and on the inner 

 with a delicate mucous membrane. Air is ad- 

 mitted to the middle ear through the Eusta- 



rinth. It consists of three parts, the vestibule, 

 the semicircular canals and the cochlea. 



The Vestibule. The vestibule is a small 

 ovoid-shaped cavity between the cochlea and 

 the semicircular canals and the cochlea. 

 entire hearing apparatus. The base of the stir- 



a 



NAMES OF THE PARTS OF THE EAR 



FIG. 1. ' 



(a) Pinna, or auricle 



(&) External auditory canal 



(c) Membrana tyuipani 



(d) Incus 



(e) Malleus 



(/) External semi-circular canal 



chian tube, which opens into the throat behind 

 the soft palate. Through the Eustachian tube 

 an equal atmospheric pressure is maintained 

 on each side of the drum membrane. Some- 

 times this balance is disturbed by forcing an 

 extra bubble of air into the middle ear when 

 one is coughing or sneezing; an uncomfortable 

 sensation is then experienced, and the hearing 

 is affected for a moment. Children often force 

 air into the middle ear by holding the nose 

 and closing the mouth and then trying to expel 

 the breath. The practice should be discour- 

 aged, as it may cause injury to the ear drum. 

 In the act of swallowing the tube is opened, 

 allowing an interchange of air and adjustment 

 of pressure. This fact is important for those 

 who ascend in airships or go down in diving 

 bells. 



The Internal Ear, or Labyrinth. The inter- 

 nal ear is a cavity having the form of a three- 

 sided pyramid, with walls and partitions of very 

 hard, compact bone. Because of its numerous 

 winding passages, it is often called the laby- 



(ff) Eustachian tube 

 (ft) Internal auditory canal 

 Fio. 2. 



(a) Head of the malleus 



(b) Incus 



(c) Plate of the stapes 



(d) Insertion of the tensor ti/mpani 



nip, or stapes bone, is set into an opening in 

 the front wall, and there are openings in the 

 other walls leading to each of the semicircular 

 canals and to the cochlea. Through minute 

 openings in its inner wall filaments of the 

 auditory nerve enter. 



The Cochlea. This little organ, shaped some- 

 what like a snail-shell, from which it takes 

 its name, is situated in front of the vestibule 

 In its center is a bonelike column, around 

 which a spiral canal winds two and a half turn* 

 At the top this canal i.s closed, but at the bot- 

 tom there are two openings, one of which lead- 

 to the vestibule. 



Semicircular Canals. These are three in 

 number; two arc in a vertical position and one 

 is horizontal. The vortical canals are placed at 

 nearly right angles to each other, one being 

 in a plane extending from front to bark and 

 the other one extending from side to side. It 

 is now generally believed that these canaU do 

 not aid the sense of hearing, but that, string'- 

 as it may seem, their function is to enable a 



