USES OF THE PARTS IN THE EAR. 335 



is the meaning of this connplex apparatus ? And 

 if the bones of the ear communicate better, what 

 is the use of the vibration coming by any other 

 course ? Let us understand, then, that the whole 

 exterior apparatus — that is to say, the parts ex- 

 terior to the labyrinth — are necessary only to 

 perfect hearing, and that when they are all gone 

 by disease, those essential parts of the organ which 

 we see suffice in the lower animals, continue to 

 receive sounds. 



The apparatus of bones and muscles connected 

 with the membrane of the tympanum (see vol. i.pp. 

 47, 48) is of more consequence than physiologists 

 allow. It is essential to perfect hearing, even when 

 the sound is conveyed through the solid bones. 

 If we hold a watch between the teeth, the sound 

 is propagated through the solid parts ; but let us 

 compress and close the outer tube of one of the 

 ears, and the sound will be increased on that side. 

 If a person, being deaf in one ear, put his watch 

 close to that ear, he will not hear the ticking ; but, 

 if at the same time he presses on the tube of the 

 other ear and closes it, he will then hear the tick- 

 ing on that side. It appears that in this experi- 

 ment, the sound propagated through the bones is 

 not given directly to the nerve, but to the mem- 

 brane and bones of the tympanum, and through 

 them back upon the nerve. The air in the outer 

 tube of the ear, being pent up by the pressure of 

 the fingers and compressed, receives the vibration, 

 reverberates on the membrane of the tympanum, 



