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per pinna, its place being commonly supplied by 

 a small tuft of feathers : the owl, however, has 

 something very similar to this part as found in 

 mammiferous animals. 



The auditory apparatus of the mammalia is in 

 general little more than a greater developernent 

 of the same parts as are found in birds. The 

 bones within their tympannm are from two to 

 six in number ; and all have a pinna except the 

 cetaceous tribes in which it would have been 

 superfluous, from the vibrations of water be- 

 ing too strong to require to be collected by this 

 means and some others, which either dwell 

 much in the water, as the shrew, or burrow un- 

 der ground, as the mole, in which, for an obvious 

 reason, it is still less called for. The shrew, 

 however, is provided with a kind of flap, like 

 that of the crocodile, the principal use of which 

 seems to be, so far from increasing the intensity 

 of the impression, to diminish it when the ani- 

 mal is under water. The great size of the pin- 

 na in some quadrupeds, and the frequency and 

 rapidity with which they move it in any direc- 

 tion, are familiar to every body; and may well 

 account, in conjunction with the complicated 

 and delicate structure of the internal parts of 

 the ear, for the extremely acute hearing which 

 they enjoy, and which is so necessary, in many 

 instances, to their security. Hence, a frequent 

 and rapid motion of the ears is, in all animals, 

 with justice regarded as indicative of a timid 

 disposition. 



