ORGANS OF SENSE. 61 



tympanum, a fibrous membrane stretched on a bony 

 frame. 



The middle ear, within the tympanum, is an irregu- 

 larly-shaped cavity, containing a chain of four little 

 bones, named from their forms the hammer, the anvil, 

 the lenticular bone, and the stirrup. This chain is at- 



FIG. 33. 



A VIEW OP ALL THE PARTS OP THE EAR. 1, Meatus or canal ; 2, the mem- 

 brana tympani ; 3, 4, 5, the bones of the ear ; 6. membrane of the foramen 

 ovale ; 7, the central part of the labyrinth (vestibule) : 8, 9, 10, the semi- 

 circular canals ; 11, 12, the channels of the cochlea ; 13, auditory nerve ; 

 14, the opening from the middle ear, or tympanum, to the throat (Eu- 

 stachian tube). 



tached at one end, the hammer and anvil, to the tym- 

 panum, and by the other, the stirrup, to the oval window. 

 The oval window and the round window are two open- 

 ings, each closed by a membrane, which establish com- 

 munication between the middle and the internal ears. 



