THE MECHANICS OF THE INNER EAR 



Everyone knows that the part of our body which in ordi- 

 nary life we call the ear and which anatomists call the pinna, 



is not the organ of hearing but a mere ap- 

 The external ear pendage to the organ. Its chief utility 



consists in the fact that it aids us in dis- 

 tinguishing sounds coming from a source in front of us from 

 sounds in our rear. We know how much more difficult it is 

 to understand the words of a speaker behind us than the 

 words of one who stands before us. We can reverse this con- 

 dition by forming of our hands leaves similar to the external 

 ears, but naturally larger and placing them opposite the ears, 

 that is in front of the opening, the auditory passage. Then, 

 sounds from the rear can enter the passage and reach the 

 tympanum with a much greater force than sounds coming 

 from the front. Animals, being able to move their external 

 ears, can use them, of course, to greater advantage than hu- 

 man beings. 



The organ of hearing — in the narrower sense of 

 the word — that is, the anatomical structure within which the 



ends of the auditory nerve fibres receive 

 The tube con- their peripheral excitations, is to be 



raining the sense found stretc h e d out along the central 

 organ is long ^ q{ & U]be which is y narrow rel- 



and narrow . , . ,, 



ative to its length. This tube is called 



by the anatomists the cochlea, because 

 it is not built in the form of a straight line, but coiled 

 up like the tube of a snail shell. The advantage of its being 

 coiled up in this way is obviously not to be sought in its 

 mechanic — or rather hydrodynamic — function. At least, no 



(O 



