ANIMAL MECHANISM. 291 



apartments, or rooms, one beyond the other, which, in 

 antomical works, have further minute subdivisions, 

 collectively, make up the labyrinth. First, the tympa- 

 num, just adverted to; Secondly, the vestibule; and 

 thirdly, the conchlca. In connexion with these are certain 

 tubes, having sundry barbarous, unintelligible names, 

 which are not remembered by one physician in a hun- 

 dred, nor, indeed, is it at all necessary. Though retained 

 in modern books of science, modern authors do not 

 seem to. have the courage to discard them. 



Behind the ear, a hard knob of bone may be felt, with 

 the finger, (mastoid process) on which that muscle is 

 fastened, which, with its fellow on the opposite side, brings 

 the head forward, as in bowing : within, this knob 

 is hollow being full of conical cells, resembling the 

 spokes of a wheel, growing smaller as they unite in one 

 pipe, which opens into the tympanum or drum barrel. 

 Physiologists agree that the use of these cells is for rever- 

 berating sound, that it may gain strength by being re- 

 flected from wall to wall, in order to excite a stronger 

 sensation when conveyed to the nerve : these are partic- 

 ularly large in some animals.* A similar piece of 

 mechanism is discoverable in the cheek bones, and even 

 the centre bone of the skull, for reverberating and 

 strengthening the voice. Lions, have large cavities in 

 the bones of their heads and faces, on purpose to increase 

 the intensity of the vibrations ; hence their charac- 

 teristic roar. 



In another direction, is the minute orifice of a cone- 

 shaped pipe, eustuchian tube, that opens with a trumpet 

 like extremity in the mouth, it being necessary to the 

 free vibration of the drum head, that the same quality of 

 air that transmits the sonorous pulsations, should also 



* In a recent letter from the venerable Dr James Thacher, of 

 Plymouth, the following curious fact is related : 



Reflection of Sound.' ' A gentleman told me, today, (May 3d, 

 1831,) that a few days since, he was passing through one of our 

 streets, where there were considerable intervals between the 

 houses, a gentleman totally blind, walking with him, assured him 

 that he knew exactly when he was passing a building, by a peculiar 

 sensation in his ears, occasioned by a different concussion of the air.' 



