THE EAR. 511 



can readily understand that a tightly stretched membrane 

 is more serviceable for collecting sounds, especially high 

 sounds, than a less taut one. 



There seems little reason, though, for attributing very 

 much to this muscle. The membrane in the telephone is 

 able to catch the widest range of tones without its stretch 

 being varied, and so there seems no difficulty in attributing 

 the same physical possibilities to its analogue in the ear. 



3. The Bones of the Ear. The vibrations of this tym- 

 panic membrane must now be carried across the middle ear 

 to the internal ear where the real sensory apparatus of the 

 ear lies. This is done by a series of three small bores, 

 known as the hammer, anvil and stirrup; or, using their 

 Ivatin equivalents, the malleus, the incus and the stapes. 

 These three bones really represent four bones ; as the incus 

 consists really of two separate bones, the incus proper and 

 the small, round orbiczdar bone which finally grows to it 

 and which serves to attach the incus to the stapes. These 

 three bones are arranged in such a way as to form a system 

 of levers, by means of which the vibrations of the tympanic 

 membrane are carried across the middle ear and with 

 mathematical precision transmitted to the inner ear through 

 the oval foramen. 



A somewhat ingenious arrangement is found in the ar- 

 ticulation of the malleus and the incus. These at their 

 point of contact fit into each other in a kind of dovetail 

 fashion, owing to the presence of peculiar interlocking 

 teeth, so arranged, however, that the least motion of the 

 malleus inwards is at once by means of these cog-like teeth 

 transmitted to the incus and so to the internal ear. A 

 violent motion, however, of the malleus outward does not 

 draw the incus with it. In this way there is prevented the 

 possibility of having the stirrup pulled out of the oval fora- 

 men in case the tympanic membrane should be suddenly 

 and forcibly pressed outward. The value of this arrange- 

 ment is evident when we remember how easily one might 



