318 THE SENSES, 



could not be stated without more anatomical references than 

 befit the occasion. 



In reptiles and amphibia the auditory organ is in every 

 case more fully developed than in fishes ; but in different 

 species to a varying extent. Thus, whilst some amphibia 

 possess a tympanum, or ear-drum, others are not so far ad- 

 vanced. Most frogs and toads have the honour to represent 

 the higher gradation. They have drums to their ears : ser- 

 pents have not. 



Certain amphibia tortoises, lizards, and crocodiles, for 

 example not only possess drums to their ears, but the or- 

 ganism called by anatomists Eustacliian tubes trumpet-like 

 prolongations effecting communication between the throat 

 and internal ear, as already explained. From reptiles we 

 arrive at birds : creatures which, anatomically regarded, 

 furnish the connecting link between reptiles and mammalia. 

 In birds the hearing organs differ but slightly from those of 

 the higher amphibia ; being almost identical with the auditory 

 apparatus of lizards and crocodiles. 



At length we come to the higher grade of animated 

 creation mammalia. Here, generally, it may be affirmed 

 that the auditory apparatus follows one scheme : that of 

 which thej hearing organs of man are typical. Exceptions 

 exist. The cetacea dolphins, whales, and porpoises have 

 no external ear. The presence of such an organ would pro- 

 bably impede the clear run of those animals through the 

 element in which they wholly reside; just as linen hung 

 over the sides of a ship, or weeds growing from the hull, 

 impede her sailing qualities. The ornithorhynchus that 

 Australian paradox is also conspicuous by the absence of 

 an external ear. 



Speaking of humanity, it may be said that all the senses, 

 except touch, minister to a corporeal and a poetic life as well. 

 This remark holds good of sound to a very high degree : 

 appreciation of sound as mere noise representing the former ; 



