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nerve destined to the perception of sound, exclusively resides. The ex- 

 ternal ear and the meatus auditorily externus may be compared to an 

 acoustic trumpet, the broad part of which, represented by the concha, 

 collects the sonorous rays which are afterwards transmitted along the 

 contracted part, represented by the meatus externus. The^concha con- 

 tains several prominences separated by corresponding depressions ; its 

 concave part is not wholly turned outward, in those who have not laid 

 their ears flat against the side of the head, by tight bandages, it is turned 

 slightly forward, and this arrangement, favourable to the collecting of 

 sound, is particularly remarkable in savages, whose hearing, it is well 

 known, is remarkably delicate. The base of the concha consists of a fibro- 

 cartilaginous substance, thin, elastic, calculated to reflect sounds and to 

 increase their strength and intensity, by the vibrations to which it is lia- 

 ble. This cartilage is covered by a very thin skin, under which no fat is 

 collected that could impair its elasticity ; these prominences are connect- 

 ed together by small muscles : these may relax it, by drawing the projec- 

 tions together, and thus place it in unison with the acute or grave sounds. 

 These small muscles within the external ear, are the musculi helicis major 

 and minor; the tngicus and anti-tragicus and the transversus auris, are 

 like the muscles on the outer part of the ear, stronger and more marked 

 in timid animals with long ears. In the hare, the fibres of these muscles 

 are most distinctly marked, their action is most apparent in this feeble 

 and fearful animal which has no resource but in flight, against the dan- 

 gers which incessantly threaten his existence, and which require that he 

 should receive early intimation of the approach of danger; hence hares 

 have the power of making their ears assume various forms, of shaping 

 them into more advantageous trumpets, of moving them in every direc- 

 tion, of directing them towards the quarter from which the noise proceeds, 

 so as to meet the sounds and collect the slightest, 



The form of the external ear, is not sufficiently advantageous in man, 

 whatever Boerhaave may have said to the contrary, to enable all the so- 

 rous rays, which in striking against it, are reflected at an angle equal to 

 that of their incidence, to be directed towards the meatus auditorius ex- 

 ternus. United, for the most part into a single fasiculus, and directed 

 towards the concha, they penetrate into the meatus auditorius externus, 

 and the tremulous motions which they excite in its osseo-cartilaginous pa- 

 rietes contribute to increase their force. On reaching the bottom of the 

 meatus, they strike against the membrana tympani, a thin and transparent 

 septum stretched between the bottom of the meatus and the cavity in 

 which the small bones of the ear are lodged. These small bones form a 

 chain of bone which crosses the tympanum from without inward, and 

 which extends from the membrana tympani to that which connects the 

 base of the stapes to the edge of the fenestra ovalis. 



An elastic air, continually renewed by the Eustachian tube, fills the 

 cavity of the tympanum: small muscles attached to the malleus and 

 stapes move these bones or relax the membranes to which they are at- 

 tached, and thus institute a due relation between the organ of hearing and 

 the sounds which strike it. It will be easily conceived, that the relaxa- 

 tion of the membrana tympani, effected by the action of the anterior mus- 

 cle of the malleus, must weaken acute sounds, while the tension of the 

 same membrane, by the internal muscles of the same bone, must increase 

 the force of the grave sounds. In the same manner, as the eye by the 

 contraction or dilatation of the pupil, accommodates itself to the light, 



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