266 Life and Health 



This membrane, the tympanic membrane, or drum mem- 

 brane, thus forms a partition between the passage of the 

 outer ear and the cavity of the middle ear. The latter is 

 a small air chamber in the petrous por- 

 tion of the temporal bone. On the bony 

 inner wall of this tympanum are two 

 openings, the round window, or foramen 

 rotundum, and the oval window, or fora- 

 men ovale, which lead into the labyrinth 



Fia.4.. Ear Bones. 



(Anterior view.) 3 417. The Eustachian Tube. The tym- 



x, malleus, or hammer; panic cavity communicates with the back 



a, incus, or anvil; 3 , part of the throat by the Eustachian tube. 



stapes, or stirrup. . 1-1 i 



1 his tube is about one and one-halt inches 

 long and lined with mucous membrane similar to that of the 

 tympanic chamber and the throat. This passage is usually 

 closed, but is opened in the act of swallowing. 



In health there is no communication between the cham- 

 ber of the middle ear and the outside, except by the 

 Eustachian tube. Thus a throat cold, with swelling of 

 the mucous membrane, is often accompanied with some 

 degree of deafness, because the swelling may block the 

 lumpen of the tube and thus prevent the free passage of 

 the air to and fro. 



> 418. The Bones of the Ear. A most curious feature of 

 the ear is the chain of tiny movable bones which stretch 

 across the cavity of the middle ear. They connect the 

 tympanic membrane with the labyrinth and serve to con- 

 vey the vibrations communicated to the membrane across 

 the cavity of the tympanum to the internal ear. 



These bones are three in number and from their shape 

 are called the malleus, or hammer ; incus, or anvil ; and 

 stapes, or stirrup. 



