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CHAPTER XII. 



DISEASES OF THE EAR. 



IN drawing the reader's attention to the structure of the eye we endeavoured to show that that 

 organ was nothing more nor less than a beautiful optical instrument designed by Nature, 

 and perfect in its adaptation to vision. The ear, on the other hand, is a most wonderfully 

 constructed acoustic instrument. Anything like a perfect description of the auditory apparatus 

 space prevents us from giving, nor in a book like the present is it required ; and we therefore 

 beg to refer the reader, if very much interested in the subject, to any good work on comparative 

 anatomy or physiology. Meanwhile, we will endeavour to render our description as concise and 

 simple as possible. 



We divide the organ of hearing, then, for convenience sake, into three portions viz. (i) the 

 external, (2) the middle, and (3) the internal ear. By the external ear is meant not only the 

 outer portion or flap of the ear, which in the dog is either erect or drooping, but also the tube 

 that leads down into the head, and into which we can thrust a probe or the finger. The 

 outer portion, then, or flap, as we all know, varies in shape, not only in different animals but 

 in different breeds of dogs. It is, properly speaking, a collector of sound, and in animals like 

 the bat, for example, reflects the collected sound down into the meatus of the ear, Sound may 

 in this instance be compared to running water ; it flows against the flap of the ear, which stops 

 its progress, and it thus flows in a backward current into the meatus. Now, the nearer any breed 

 of dog approaches in descent to the wild dog, the more will his ear be pricked. We have only 

 to instance the Yack dogs or Esquimaux. 



Those dogs, too, will have pricked ears, or partially erect, who have to depend much upon 

 their sense of hearing to enable them to perform their duties as the servants of mankind. 



The organ of hearing proper is placed deeply down in the centre of the petrous portion of 

 the temporal bone. The canal which leads from the outside to the middle ear is terminated by a 

 thin skin or membrane which partitions it off, as it were, from the middle ear. 



This membrane is, in other words, the parchment cover of the kettledrum of the ear. This 

 membrane is elastic, and vibrates to every sound. 



Now, if you were to put a needle through this membrane, the point of it would enter the 

 tympanum or drum, or middle ear. Herein there is a little chain of bones which need not here 

 be particularised further than to say they stretch from the membrane across the drum, one 

 end being attached to this, and the other to the membrane dividing the drum from the internal 

 or ear proper ; and we will see the purpose of this chain presently. A tube opens into the drum. 

 This is called the Eustachian tube. It is an air-pipe, and supplies the drum with air. It 

 runs downwards and forwards, and opens into the back part of the throat. When we hold the 

 nose and go through the motions of swallowing, we hear a crackling in the ears ; this is caused 

 by the air rushing up that tube and distending the drum of the ear. When this tube is closed 

 partially, as when one has a cold, or permanently from inflammation, no air can get to this 

 drum, the outer membrane cannot vibrate, and the person or dog becomes deaf. 



