HEARING. 



669 



by which as well as by the vibrations of the 

 bones, the air in the tympanum is made to 

 vibrate, and that cavity being closed the sono- 

 rous vibrations are reflected from its walls so as 

 to give rise to the augmentation of the sound. 



Autenrieth and Rerner believed the cochlea 

 to be that part of the auditory apparatus by 

 which we perceive what the French call the 

 " timbre" of sounds; that quality, namely, 

 which depends on the nature of the material 

 of which the sounding body is constituted, 

 as well as on its form and size, and in some 

 degree on the manner in which sound is 

 elicited from it; and they considered it the 

 office of the vestibule to convey to the sen- 

 sorium the pitch and strength of sounds. Their 

 opinion as to the function of the cochlea was 

 founded on some experiments as to the extent 

 to which ceitain of the lower animals were 

 affected by particular instruments of music : 

 the results obtained from these experiments, 

 when taken in connexion with certain dif- 

 ferences in the form and other characteristics 

 of the cochlea in those animals, led these 

 authors to the conclusion that " those ani- 

 mals alone seemed to perceive a difference 

 of the ' timbre' of sounds of pretty uniform 

 pitch and loudness, in whom the cochlea was 

 very long and projected considerably into the 

 cavity of the tympanum, and was not much 

 concealed by the surrounding bony substance. 

 Thus it appeared that a dog (the cochlea of 

 dogs being longer than that of cats), upon 

 hearing a certain note of the clarionet, set up 

 a howl, but seemed in no way affected at 

 hearing the same note from the flute or violin ; 

 but the cat continued undisturbed, although a 

 variety of instruments was sounded in her 

 hearing. A rabbit (in which the cochlea is 

 prominent) ran away at the note C elicited from 

 a slass tumbler or from a string, but remained 

 still when the same note was sounded even 

 more loudly by the flute/'* But it is abun- 

 dantly evident that these experiments do not 

 fairly lead to the conclusion which these phy- 

 siologists endeavoured to establish; for, as 

 Weber has remarked, it is one thing to be dis- 

 agreeably affected by the peculiar tone of a 

 given note in an instrument of music, and 

 another thing to distinguish the timbre of the 

 notes of different musical instruments. As 

 well might we conclude that dogs excel in the 

 power of distinguishing scents and savours, 

 because the smell and taste of spirits of wine 

 seem to be peculiarly disagreeable to them, 

 and they reject instantly, although hungry, 

 any food offered to them with which that has 

 been mixed. 



It seems evident that the cochlea is an in- 

 dication of a very advanced condition of the 

 organ of hearing ; beyond this we can arrive at 

 no definite conclusion in the present state of 



* See these experiments quoted at greater length 

 in Weber's paper before referred to. Autenrietb/s 

 paper is to be found in Reil's and Autenrieth's 

 Archiv. fur die Physiologic, B. ix. 1809; and 

 contains much valuable and highly interesting 

 matter relative to all the parts of the organ of 

 hearing in several of the Mammalia. 



our knowledge, unless indeed we admit the 

 very general one of Weber, that it is the pri- 

 mary seat of those auditory impressions which 

 are conveyed through the vibrations of the 

 cranial bones. But this view, however pro- 

 bable, and supported by much sound reasoning, 

 throws no light on the object of the peculiar 

 form and mechanism of the cochlea. We 

 must not omit to notice that a portion of the 

 vestibule is regarded by Weber as performing 

 a similar function to that of the cochlea, and 

 on similar grounds. That portion which is 

 known under the name of the sacculus is so 

 adherent to the bony wall of the vestibule, 

 corresponding toihejoveahemispherica, accord- 

 ing to Scarpa, that it cannot be separated 

 without laceration, and consequently it seems to 

 be better adapted to receive the sonorous vibra- 

 tions which are conveyed by the cranial bones. 



The remaining parts of the labyrinth, namely, 

 the three semicircular canals and the common 

 sinus, are most affected by those sounds which 

 are conveyed through the external meatus : it 

 seems evident at least that they must be more 

 affected than the cochlea from the connexion 

 between the membrana tympani and fenestra 

 ovalis through the chain of tympanic ossi- 

 cles, by which that membrane is brought 

 into direct communication with the perilymph 

 surrounding the membranous labyrinth. On 

 the other hand these parts are badly adapted 

 to receive the impression of vibrations direct 

 from the cranial bones, being separated from 

 the corresponding osseous parts by the peri 

 lymph, and that part of the auditory nerve 

 which is distributed to them, having no con- 

 nexion with the bone. An experiment of 

 Weber illustrates the relation of the perilymph 

 to the membranous labyrinth, and shows that 

 an impulse upon the membrana tympani is 

 capable of affecting it. In some birds, the 

 falcon for example, the semicircular canals are 

 so large, that the membranous canals may be 

 easily seen. If in such a bird one osseous 

 semicircular canal be opened by a small open- 

 ing, care being taken not to injure the mem- 

 branous canal, and then we press the mem- 

 brane of the tympanum inwards, at each com 

 pression we observe the water contained in the 

 bony canal to flow out with a jerk. He there- 

 fore concludes that the sonorous undulations 

 conveyed by the cranial bones are communi- 

 cated more immediately to the nerve of the 

 cochlea, but those conveyed by the external 

 meatus to the nerve of the vestibule. 



The semicircular canals are remarkable for 

 the constancy of their number, and of their re- 

 lative position with respect to each other, in all 

 animals in whom they are found. They exist 

 in almost all fishes, and in all the other vertebrate 

 classes, and in these they are never less than 

 three in number, two of which are always 

 placed vertically and one horizontally. The 

 opinion that the arrangement of these canals 

 has reference to conveying the sensation of the 

 direction of sounds, I find expressed by Au- 

 tenrieth and Kerner in the paper already re- 

 ferred to. "In no animal," they say, " are these 

 canals ever more or fewer on each side than 



