HEARING. 313 



we meet with a concha, or external ear, distinctly marked; 

 and the utility of this part, in catching and coliectinj^ the 

 sonorous undulations of the air, may be inferred from the 

 circumstance, that a large and very moveable concha is ge- 

 nerally attended with great- acuteness of hearing. This is 

 more particularly the case with feeble and timid quadrupeds, 

 as the hare and rabbit, 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 pursuers; while, on 

 the contrary, the ears of predaceous animals are directed 

 forwards, that is, towards the objects of their pursuit. This 

 difference in direction 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 leading 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 preventing the en- 

 trance of any quantity of water.* It is apparently with the 

 same design that in the Seal the passage makes a circular 

 turn; and that, in the Ornithorhyncus 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 other cetacea, are en- 

 closed in a bone of extraordinary hardness, which, instead 

 of forming a continuous portion of the skull, is connected to 

 it only by ligaments, and suspended in a kind of osseous ca- 

 vity, formed by the adjacent bones. The cochlea is less de- 

 veloped than in quadrupeds, for it only takes one turn and 

 a half, instead of two and a half. The existence of the se- 



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

 sounds reach the internal organ is the Eustachian tube. 



Vol. II. 40 



