314 THE SENSORIAL FUNCTIONS. 



micircular canals in the cetacea was denied by Camper; but 

 they have since been discovered by Cuvier. 



Several quadrupeds which are* in the habit of burrowing, 

 or of diving, as the Sorex fodiens, or water-shrew, are fur- 

 nished with a valve, composed of a double membrane, capa- 

 ble of accurately 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 displayed in 

 this as in every other department of the animal economy: 

 every part, however minute, of the organ of this important 

 sense, being expressly adapted, in every species, to the par- 

 ticular circumstances of their situation, and to that degree of 

 acuteness of perception, which is best suited to their respec- 

 tive wants and powers of gratification.! 



* Geoffrey St. Hilaire; Mmoires du Museum, i. 305. 



f The Comparative Physiology of VOICE, a function of which the object, 

 in animals as well as in man, is to produce sounds, addressed to the ear,* and 

 expressive of their ideas, feelings, desires and passions, forms a natural se- 

 quel to that of Hearing? but Sir Charles Bell having announced his intention 

 of introducing it in his Treatise on the Hand, I have abstained from enter- 

 ing into this extensive subject. 



