- 258 , Mr. R. Moon on the Functions of the Membranous 



tres eteudues : ces oscillations s'affaiblissent ensuite peu h peu ; 

 un moment avant de cesser, il n'y a plus qu'un leger tremblement 

 qui represente tout a fait le tremblement de la ttte qui s' observe 

 dans certains vieillards." 



Affections such as those last referred to I conceive to arise 

 from paralysis (it may be only partial) of the semicircular canals 

 of one ear. 



III. I now propose to consider the question whether the func- 

 tions above described exhaust the purposes of the membranous 

 labyrinth — in other words, whether the membranous labyrinth 

 actually forms part of the organ of hearing. 



That, in man and those animals which possess a cochlea, all 

 aerially conveyed sounds are perceived through the agency of the 

 cochlea alone I think there cannot be the smallest doubt. The 

 construction of the tympanal membrane, the bones of the ear, 

 and the two foramina opening from the tympanal cavity into the 

 labyrinth, abundantly prove that motion of the fluid in the cochlea 

 from the round aperture towards the oval aperture, and vice versa, 

 is the special effect which aerially conveyed waves are calculated 

 to produce ; and even if the nervous filaments of the membranous 

 labyrinth hung loose in the perilymph which surrounds the latter, 

 I cannot see that they would be in any way affected by such 

 motion of the fluid in the cochlea. Still less can this be the case 

 in the actual position of the extremities of the nervous filaments 

 within the membranous labyrinth. 



But it is not so clear that the nerves within the membranous 

 labyrinth are not affected by undulations propagated through the 

 bone of the skull — as, for instance, when a musical box is placed 

 on the top of the head ; or rather it is not so clear whether these 

 nerves do not, under the circumstances supposed, aid in the pro- 

 duction of that sensation which we attribute to sound. 



I am strongly inclined to take the negative view of the ques- 

 tion last stated, and to regard the cochlea on the one hand, 

 and the canals and membranous labyrinth on the other, as totally 

 independent organs which, for constructive and, it may be, for 

 other purposes, are locally connected — just in the same way as 

 the ear and the nostril are connected, though the former is in no 

 degree ancillary to the sense of smell*. This, no doubt, is tan- 

 tamount to the assumption that animals destitute of a cochlea 

 are incapable of the perception of sound. It is to be observed, 

 however, that it is not denied that when a sounding body is ex- 

 cited, animals in its neighbourhood which are possessed of sac 

 and utricle only, or of those appendages and semicircular canals, 



* Mr. Wharton Jones testifies to a characteristic difference between the 

 nerves of the cochlea and those of the membranous labyrinth. I do not 

 desire, however, to urge too far this consideration. 



