.depth, and separated from the outer part of the head, by a cavity and a 

 canal along which the sonorous rays are transmitted, after having been 

 collected into fasciculi by trumpets situated on the outside. 



This kind of natural analysis of the organ of hearing, is well calcula- 

 ted to give accurate notions on the -nature and importance of the func- 

 tions fulfilled by each of its parts. ^But in the investigation of the uses 

 and of the relative importance of the auditory apparatus, morbid anatomy 

 furnishes data of an equal value with those obtained from comparative 

 anatomy. 



CXXIII. The external ear may be removed, with impunity, in man, 

 and even in animals in which its form is more advantageous ; the hearing 

 is, at first impaired, but at the end of a few days, recovers its wonted de- 

 licacy. The complete obliteration of the meatus auditorius externus, is 

 attended with complete deafness. It is not essentially necessary for the 

 mechanism of hearing 1 , that the membrana tympani should be whole ; 

 persons in whom it has been accidentally ruptured, can force out smoke 

 at their ears, without losing the power of hearing; it may be conceived, 

 however, that if instead of having merely a small opening that would not 

 prevent its receiving the impression of the sonorous rays, nor its being 

 acted upon by the handle of the malleus, the membrana tympani were al- 

 most entirely destroyed, deafness would be the almost unavoidable conse- 

 quence*. If, in consequence of the obstruction of the Eustachian tube, 

 the air in the tympanum is not renewed, it loses its elasticity and com- 

 bines with the mucus within the tympanum. The cavity of the tympa- 

 num is then, in the same condition as an exhausted receiver, in which 

 the sonorous rays are transmitted with difficulty. It has been thought, 

 that the use of the Eustachian tube was, not only to renew the air con- 

 tained in the tympanum, but also transmit the sonorous rays into that ca- 

 vity. In listening attentively, we slightly open our mouth 5 in order, it is 

 said, that the sound may pass from this cavity into the pharynx and 

 thence reach the organ of hearing. This explanation is far from satis- 

 factory, for the obliteration of the meatus auditorius externus is attended 

 with complete deafness, which would not happen, if the Eustachian tubes 

 transmitted the sonorous rays. When a man listens attentively, and 

 with his mouth open, the condyles of the lower jaw, situated in front of 

 the external auditory meatus, being depressed and brought forward, the 

 openings are evidently enlarged, as may be ascertained by puttiug the 

 the little finger into one's ears, at the moment of depressing the lower 

 jawf. The luxation of the small bones of the ear, or even their complete 

 destruction, does not occasion deafness, the only consequence is a con- 

 fusion in the perception of sounds When, however, the stapes, the base 

 of which rests on the greatest part of the fenestra ovalis, or when the 



* We find that a temporary obstruction of the Eustachian tube in guttural angina is 

 sufficient to occasion a considerable degree of deafness. In such a case, the inflamma- 

 tion of the mucous membrane of the pharvnx extends itself to that which lines the tube, 

 of which it is a continuation ; and the effect that the inflammation produces on tne 

 function of the organ are proportionate to the extent to which it advances in the differ- 

 ent compartments of the internal ear. Copland. 



f The open state of the mouth in an attentive listener by no means proves that the 

 sonorous rays are introduced along the Eustachian tube. Indeed, if such were the case, 

 the aerial pulsations arriving by this direction would strike the tympanum in an opposite 

 direction to those that are admitted by the external passage, and thus render the hear- 

 ing confused. The purpose, therefore, which the Eustachian tube performs is nothing 

 more than to allow the renewal of the air within the tympanum. Copland, 



