HEARING. 443 



parts of the organ of hearing in the Whale and 

 other cetacea, are enclosed in a bone of extra- 

 ordinary 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 cavity, formed by the adjacent bones. 

 The cochlea is less developed than in quad- 

 rupeds, for it only takes one turn and a half, 

 instead of two and a half. The existence of the 

 semicircular canals in the cetacea was denied 

 by Camper ; but they have since been disco- 

 vered by Cuvier. 



Several quadrupeds, which are in the habit of 

 burrowing, or of diving, as the Sorex fodiens, or 

 water-shrew, are furnished with a valve, com- 

 posed of a double membrane, capable of accu- 

 rately closing the external opening of the meatus, 

 and protecting it from the introduction of water, 

 earth, or other extraneous bodies.* In like 

 manner the external ear of the Hippopotamus, 

 which feeds at the bottom of rivers, is guarded 

 by an apparatus which has the effect of a valve. 



We find, indeed, the same provident care dis- 

 played in this, as in every other department of 

 the animal economy : every part, however mi- 

 nute, of the organ of this important sense, being 

 expressly adapted, in every species, to the par- 

 ticular circumstances of their situation, and to 



* GeofFroy St. Hilaire ; Memoiies du Museum, i, 305. 



