INTRODUCTION. xxiii 
in those, where the organ is disclosed, the nerves, which take 
their origin from it, are far from being so numerous, so large, 
or so expanded as in the quadrupeds. We may therefore 
regard touch in man, smell in the quadruped, and sight in 
birds, as respectively the three most perfect senses which 
exercise a general influence on the character. 
After sight, the most perfect of the senses in birds appears 
to be hearing, which is even superior to that of the quadru- 
peds, and scarcely exceeded in the human species. We per- 
ceive with what facility they retain and repeat tones, successions 
of notes, and even words; we delight to listen to their un- 
wearied songs, to the incessant warbling of their tuneful affec- 
tion. Their ear and throat are more ductile and powerful 
than in other animals, and their voice more capacious and 
generally agreeable. A Crow, which is scarcely more than the 
thousandth part the size of an ox, may be heard as far, or 
farther ; the Nightingale can fill a wider space with its music 
than the human voice. This prodigious extent and power of 
sound depend entirely on the structure of their organs ; but 
the support and continuance of their song result solely from 
their internal emotions. 
The windpipe is wider and stronger in birds than in any 
other class of animals, and usually terminates below in a large 
cavity that augments the sound. The lungs too have greater 
extent, and communicate with internal cavities which are 
capable of being expanded with air, and, besides lightening 
the body, give additional strength to the voice. Indeed, the 
formation of the thorax, the lungs, and all the organs connected 
'yith these, seems expressly calculated to give force and dura- 
tion to their utterance. 
Another circumstance, showing the great power of voice in 
birds, is the distance at which they are audible in the higher 
J'cgions of the atmosphere. An Eagle may rise at least to the 
height of seventeen thousand feet, for it is there just visible. 
Flocks of Storks and Geese may mount still higher, since, not- 
withstanding the space they occupy, they soar almost out of 
®'ght; their cry will therefore be heard from an altitude of 
