3yt» THE SENSORIAL TUNCTIONS. 



Iso in this class alone that we meet with a concha, 

 or external ear, distinctly marked ; and the utility 

 of this part, in catching and collecting the sonorous 

 undulations of the air, may be inferred from the 

 circumstance, that a large and very moveable 

 concha is generally attended with great acuteness 

 of hearing. This is more particularly the case with 

 feeble and timid quadrupeds, as the Hare and 

 Rabhit, which are ever on the watch to catch the 

 most distant sounds of danger, and whose ears are 

 turned backwards, or in the direction of their pur- 

 suers ; while, on the contrary, the ears of preda- 

 ceous animals are directed forwards, that is, towards 

 the objects of their pursuit. This difference in di- 

 rection is not confined to the external ear, but is 

 observable also in the bony passage leading to the 

 tympanum. 



The Cetacea, being strictly inhabitants of the 

 water, have no external ear ; and the passage lead- 

 ing to the tympanum is a narrow and winding tube, 

 formed of cartilage instead of bone, and having 

 a very small external aperture. In the Dolphin 

 tribe the orifice will barely admit the entrance of a 

 pin ; it is also exceedingly small in the Dugong ; 

 these structures being evidently intended for pre- 

 venting the entrance of any quantity of water.* It 

 is apparently M'ith the same design that in the Seal 

 the passage makes a circular turn ; and that, in 

 the Ortiithorhynchus paradoxus, it winds round the 

 temporal bone, and has its external orifice at a 

 great distance from the vestibule. The internal 

 parts of the organ of hearing in the Whale and 



* It is probable that in these animals the principal channel by 

 which sounds reach the internal organ is the Eustachian tube. 



