THE SENSE OF HEARING. 229 



the sound would be flat, and the head liable to be ruptured. 

 When this tube is obstructed by the swelling of its lining 

 membrane from cold, or the accumulation of secretion in the 

 passage, deafness is the consequence. This passage is about 

 an inch and a half in length, and widens from the ear to the 

 throat like a trumpet. When deafness occurs from com- 

 plete closure of this tube, hearing may be restored by per- 

 forating the membrane of the drum. We may ascertain 

 with a good degree of certainty whether deafness arises from 

 this cause, by placing a watch between the teeth, if its mo- 

 tions are audible, we may conclude that the essential organ 

 of hearing is unaffected. 



8. Bones of the .Ear.- These are four in number, and are 

 so connected with each other in the drum, that they serve 

 to transmit vibrations of the membrane of the tympanum to 

 the internal ear/ From their shape, they are called the 

 mallet, the ajivil, the orbicular, and the stirrup bones, and are 

 exhibited in nearly the natural size in the following cut. 

 Mallens, Incus, and Orbiculare, Stapes. 

 Fig. 3. 



Bones of the ear. 



These bones are very hard and brittle, have no cartilage on 

 their articular surfaces like other bones ; neither are they 

 furnished with ligaments or synovia, but their dry and 

 polished surfaces are accurately fitted to each other in the 

 form of a bent lever ; and in this way, being connected and 

 held together by the little muscles, by which they are moved 

 and attached to each other, the intensity of vibration which 

 they receive from the membrane of the drum is not blunted. 



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