70 EAR. 



A. To look upon, anatomists say, they are more 

 like what we are accustomed to call machinery, than 

 almost any thing beside in animal bodies. It is, as if, 

 upon cutting open a drum, we should find a chain of 

 little rods hinging one upon another across the whole 

 length of the barrel from head to head. It has been 

 suggested, that they probably tighten or loosen the 

 drum heads, with which these bones communicate ; 

 just as the. musician loosens or strains up the head of 

 his drum by means of the cords and leathers, which 

 we see on the outside. By stretching or loosening 

 the head, he strengthens or weakens his sounds ; and 

 the little bones are supposed by many anatomists, to 

 produce the same effect. 



B. They make a tuning apparatus then, it seems, 

 for our ears. 



T. Their chief use is generally conceived to be, 

 to conduct the sound from one drum head to the 

 other. Do you know that every drum has a hole in 

 the barrel ? and are you acquainted with the reason ? 



B. It would seem necessary to admit the air into 

 the drum ; otherwise, the air would not be the same 

 on both sides of the drum head, and whichever should 

 press the most, — the external, or the internal air, — it 

 would crowd against the skin and be injurious to the 

 sound ; at least, I suppose it is for some such reason, 

 that the hole is made. 



T. Why then are we not subject to some incon- 

 venience in the ear, when the barrel has no commu- 

 nication with the air by means of the external ear, on 

 account of the membrane of the tympanum, which 



