CHAPTER XXII 



THE EAR 



ALTHOUGH externally the ear does not appear to be so 

 delicate an organ as the eye, yet as a sense organ it is scarcely 

 less intricate in structure, or necessary in daily life. It has 

 been noted that the eye is quite protected in its rather deep 

 socket; but the ear is yet more secure, being set deeply into 

 and almost surrounded by the temporal bone of the cranium. 

 For convenience in description it is treated as though in three 

 parts, the outer, the middle, and the inner ear. 



The Outer Ear. The portion of the ear which protrudes 

 on the side of the head is made up largely of skin, containing 

 several small pieces of cartilage which give it shape. In many 

 animals the outer ear is large and acts as an organ for gathering 

 sound waves and leading them against the ear drum inside; 

 in man, however, this use of the outer ear is practically gone, 

 and it has no special function. Muscles for moving it, which 

 are highly developed in many and especially in four-footed 

 animals, are present in man also, but have degenerated 

 through lack of use. The old-fashioned ear trumpet was 

 merely an auxiliary contrivance for collecting more sound 

 waves and conducting them into the ear. 



The canal leading into the head is called the external 

 auditory meatus; Fig. 181. This comes to an abrupt ending 

 against a thin membrane, the ear drum, or tympanic mem- 

 brane. The canal dips downward a little as it goes inward, 

 and this fact explains how it is that water may get into the 

 ear when one has the head under water when swimming, and 

 why it can only be gotten out by tipping the head to one side 



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