HEARING. 



571 



No conclusions can be derived from the 

 experiments of Flourens with respect to the 

 functions of the several parts of the labyrinth. 

 The effects of disease had already sufficiently 

 indicated the relative importance of the dif- 

 ferent parts of the ear, and even to a certain 

 extent of those of the labyrinth. Thus we 

 knew that stoppage or destruction of the ex- 

 ternal parts does no more than impair the sense 

 of hearing, and that so long as the labyrinth 

 remains perfect, or at least the vestibule, the 

 sense is not destroyed. Sound may be con- 

 veyed to the auditory nerve through the bones 

 of the head, as may be proved by the sen- 

 sation of sound produced by the application 

 of a tuning-fork in vibration to the teeth or 

 to some one of the cranial bones. By a parity 

 of reasoning, Flourens having successively de- 

 stroyed the several parts of the ear in pigeons, 

 inferred that the nervous expansion in the ves- 

 tibule was the part of the organ most essential 

 to audition : " that in strictness, it is the only 

 indispensable part, for all the others may be 

 removed; yet if this continue, audition is not 

 destroyed." Partial destruction of the nervous 

 expansion in the vestibule only partially destroys 

 the sense, and complete destruction of this ex- 

 pansion involves total deafness. The vestibule 

 maybe laid open without any very considerable 

 alteration in the sense ; but rupture of the semi- 

 circular canals rendered the hearing confused 

 and painful, and was moreover accompanied 

 with a quick and violent tossing of the head.* 



One can scarcely imagine vivisections less 

 likely to lead to useful results than those 

 which involve the exposure of the deep-seated 

 internal parts of the ear, a dissection which 

 even on the dead subject demands no ordinary 

 skill ; nor can we refrain from expressing our 

 opinion that had M. Flourens never attempted 

 these experiments, physiology would have been 

 none the worse, and our respect for his hu- 

 manity would have been all the greater. 



II. Of the ac ccssory parts of the organ. 

 We shall consider in succession the parts which 

 the external ear the tympanum, its membrane 

 and ossicles, and the Eustachian tube, play in 

 the process of audition. 



The external ear may be regarded as consist- 

 ing of two parts, the auricle and the meatus 

 auditorius externus. The complete develope- 

 ment of the former is found only in Mammi- 

 ferous animals, and exists pretty generally 

 throughout the class ; with, however, consider- 

 able diversity of form, varying from an almost 

 flat cartilaginous lamella, scarcely at all under 

 the influence of its muscles, to an elongated 

 funnel-shaped ear-trumpet, very moveable and 

 completely at the command of numerous large 

 muscles. Man and the Quadrumana are at one 

 extremity of this scale ; the Solipeds, Rumi- 

 nants, and Cheiroptera at the other. Some, 



pressure of the stapes must serve to moderate the 

 tension of the fluid within the vestibule, which 

 serves to convey the impression. The cochlea seems 

 to be pretty evidently a micrometer of sound. See 

 Med. Lit. p. 98. 



* Conditions de 1'Audition in Experiences sur le 

 Systeme nerveux, p. 49. Par. 1825. 



however, are devoid of the auricle, as the mole, 

 the zemni-rat, the mole-rat, the seal, the walrus, 

 &c. It is said that those animals which are 

 remarkable for the large developement of the 

 auricle are almost all timid or nocturnal, and 

 consequently require an acute sense of hearing. 

 That the auricle performs the office of an 

 acoustic instrument to collect and reinforce the 

 sounds which fall upon it, cannot be doubted 

 in those cases in which it is large and fully 

 developed, as in the horse, ass, &c. Here, 

 indeed, we see that the animal employs it as 

 we might expect such an instrument would be 

 used ; the open part is directed towards the 

 quarter whence the sound comes, and continues 

 so directed as long as the animal appears to listen. 

 So far, however, from this part being mainly the 

 instrument for enabling the animal to judge of 

 the direction of sound, it appears to me that 

 it cannot be applied to its full use until the 

 direction of the sound has been in some mea- 

 sure determined ; until the hearing-trumpet has 

 been favourably placed with respect to the 

 quarter whence the sound emanates, its value 

 is not fully experienced. If we watch the 

 movements of the auricle of a horse, we shall 

 see that he uses it altogether for concentrating 

 sounds from particular quarters: when he moves 

 it about quickly, it often seems as if he were 

 feeling for sounds coming from certain direc- 

 tions, having already acquired a tolerable 

 notion, if I may so speak, as to what those 

 directions are. Treviranus,* however, thinks 

 that the reinforcement of the sound is not its 

 principal use : " to what end," he asks, " have 

 its various eminences and depressions been 

 formed, if it have no other use than this, and 

 why are these particularly developed in the 

 human ear, which can have little or no in- 

 fluence as an ear-trumpet in increasing the 

 influence of sounds?" He supposes that in 

 the lower animals, but especially in man, the 

 auricle serves more for forming a judgment 

 respecting the direction of sounds than for 

 assisting in hearing. We cannot understand in 

 what way the fixed auricle of man can aid for 

 this purpose, being almost immoveable, and in- 

 deed altogether so for the purposes of collect- 

 ing sonorous undulations from different quar- 

 ters; nor indeed does it appear that the opinion 

 in question of Treviranus is any thing more 

 than a mere hypothesis. A remark of Mr. 

 Gough, the author of a highly interesting 

 paper in the Manchester Memoirs " on the 

 method of judging by the ear of the position 

 of sonorous bodies," offers a strong argument 

 against this notion. He observes that what- 

 ever may be the direction of a sound in the 

 open air, as soon as it enters the auditory pas- 

 sage, it is compelled to follow the course of 

 that duct until it reaches the apparatus in which 

 the sense of hearing resides.f 



The experimental researches of Savart throw 

 some light upon the function of this part of 

 the auditory apparatus.! These experiments 



* Loc. cit. B. ii. p. 137. 



t Manchester Memoirs, New Series, vol. v. 



i Majendie's Journal de Physklogie, torn. iv. 



