192 SENSORIAL FUNCTIONS. 



under the tympanum containing air ; this part of the ap- 

 paratus being obviously fitted for atmospheric hearing, as 

 the other apparently is for aquatic hearing only. 



596. What clear marks of design and what wonderful 

 traces of wisdom and goodness is evinced in the adaptation 

 of these parts to the wants and habits of these poor cold- 

 blooded animals ! Truly, " an undevout naturalist must 

 be mad." 



597. Hearing in Birds. In the birds there is a cavity 

 beyond the tympanum, as in man, and the tympanum it- 

 self, instead of being on the outside, lies concealed in a 

 short tube, without any external ear, thus placing this class, 

 in respect to the auditory apparatus, between the amphibia 

 and quadrupeds. 



598. The ear of man may be taken as an example of 

 the interior structure of this organ in the whole of the oth- 

 er mammalia. In quadrupeds, the chief peculiarity in other 

 respects is in the size and form of the external ear ; and 

 from a comparison of the relative size of this part in the 

 various tribes, it has been inferred, that it bears a tolerably 

 constant proportion to the degree of acuteness of hearing, 

 and consequently, that it contributes essentially to that 

 faculty. Thus in the rabbit, where the cochlea is uncom- 

 monly long, and somewhat trumpet-shaped, the hearing is 

 remarkably acute. In the dog, and horse, this part is well 

 developed, and we accordingly find a corresponding acute- 

 ness of hearing. 



599. In animals with long ears, there are muscles for 

 the purpose of erecting them or turning them toward the 

 point whence the sound proceeds ; and thus they have the 

 effect of an ear-trumpet, in concentrating the sonorous 

 undulations, from whatever direction they come. Every 

 one must have observed the employment of this faculty 

 in the horse, which always turns his ear in the di- 

 rection of the sound. Hence it is that the leaders of coach- 

 horses turn their ears forward, while those behind them 



What is said of the ears of birds? What is the construction of the in- 

 ternal ear of the mammalia ? Is there any relation between the external 

 ears of animals and their sense of hearing ! Do men ever possess the 

 Dower of turning their ears ? 



