108 777 E HUMAN I1ODY. 



made chiefly of cartilage. There are three little muscles 

 attached to the external ear, and some people can move 

 it. Most people can not. 



3, The tube is called the external auditory canal. It 

 is an inch long, and ends at the membrane of the tym- 

 panum. 



4, The membrane of the tympanum, or drum-head, sepa- 

 rates the middle from the external ear. The cavity of 

 the middle ear is called the tympanum, or drum. It con- 

 tains the small bones of the ear. It is connected with 

 the back part of the throat by a tube, called the Eustachian 

 tube. 



5, The internal ear is beyond the middle ear, deep in a 

 bone of the skull. In it are the endings of the nerve of 

 hearing. 



HOW WE HEAR. 



6, Sound is a vibration which can be perceived by 

 the ear. Commonly as it reaches the ear it is a vibra- 

 tion of the air. The waves of 

 air enter the external auditory 

 canal, and strike the drum- 

 head. They make the drum- 

 head vibrate. 



7. Across the cavity of the 

 drum, from the drum-head to 

 Fi 65 the opposite wall, the three 



BONES OF THE LEFT EAR, SEEN little bones of the ear the 



FROM THE INSIDE. -1. Hammer hammer " the " Elivil " Elld 

 2. Anvil, a. Stirrup. 4. Stapedius. 



the "stirrup are stretched 



in a chain. The hammer is joined to the drum-head 

 and to the anvil, and the anvil to the stirrup. 



8, When the drum-membrane vibrates, these little bones 



