The Sense op Hearing 125 



bones consist not of bony substance, but of cartilage, sub- 

 cartilage, and even of muscles. 



With reference to this speculative theory upon the 

 subject of the ear of birds, Sir Charles Bell justly remarks 

 that ' ' the only effect of this hypothesis is to make us lose 

 sight of the principle which ought to direct us in the 

 observation of such curious structures, as well as of the 

 conclusions to which an unbiassed mind would come. 

 The matter to be explained is simply this : the chain of 

 bones in the ear, which is so curiously adapted in the 

 mammalia to convey the vibrations of the membrane of 

 the tympanum to the nerve of hearing, is not found in 

 the organ of hearing of birds ; but there is substituted a 

 mechanism entirely different. They choose to say that 

 the incus, one of the bones of the chain, is wanting in the 

 bird. Where shall we find it ? they ask. Here it is in 

 the apparatus of the jaw or mandible ; in that bone which 

 is called Os quadratum." 



From this mode of enquiry we find that the sense of 

 hearing is enjoyed in an exquisite degree in birds ; that 

 the organ of the sense is not imperfect, but is adapted to 

 a new construction, and a varied apparatus, suited to the 

 condition of the bird ; and that there is no accidental dis- 

 location, or substitution of something less perfect than 

 what we find in other classes of animals. 



The internal parts of the ear in birds are much less com- 

 plicated than in man and quadrupeds. We have little 

 doubt that the provision made for rendering birds more 

 buoyant, consisting of air-vessels extended from the lungs 

 throughout the body, and even to the bones themselves, 

 contributes to render the vibrations of the air more 

 distinct, mufHed as they must always partially be by the 

 feathers of the bird. 



The faculty of imitating sounds possessed by certain 

 birds proves that their hearing must be exceedingly deli- 

 cate ; and though we suspend our belief of the great 

 musical talents which some birds are said to have derived 

 from education, we find many well-attested instances of 

 a delicate ear in species by no means remarkable for vocal 

 execution. 



