OF ANIMAL CODIES. 
107 
of notice) these rings are not complete, that is, are not car¬ 
tilaginous and stiff all round; but their hinder part, which 
is contiguous to the gullet, is membranous and soft, easily 
yielding to the distensions of that organ occasioned by the 
descent of solid food. The same rings are also bevelled off 
at the upper and lower edges, the better to close upon one 
another, when the trachea is compressed or shortened. 
The constitution of the trachea may suggest likewise an¬ 
other reflection. The membrane which lines its inside, is, 
"perhaps, the most sensible irritable membrane of the body. 
It rejects the touch of a crumb of bread, or a drop of water, 
with a spasm which convulses the whole frame; yet, left to 
itself, and its proper office, the intromission of air alone, 
nothing can be so quiet. It does not even make itself felt; 
a man does not know that he has a trachea. This capaci¬ 
ty of perceiving with such acuteness, this impatience of 
offence, yet perfect rest and ease when let alone; are pro¬ 
perties, one would have thought, not likely to reside in the 
same subject. It is to the junction, however, of these al¬ 
most inconsistent qualities, in this, as well as in some other 
delicate parts of the body, that we owe our safety and our 
comfort;—our safety to their sensibility, our comfort to 
their repose. 
The larynx, or rather the whole windpipe taken together, 
^for the larynx is only the upper part of the windpipe,) be¬ 
sides its other uses, is also a musical instrument, that is to 
say, it is mechanism expressly adapted to the modulation of 
sound; for it has been found upon trial, that, by relaxing 
or tightening the tendinous bands at the extremity of the 
windpipe, and blowing in at the other end, all the cries 
and notes might be produced of which the living animal 
was capable. It can be sounded, just as a pipe or flute is 
sounded. Birds, says Bonnet, have at the lower end of 
the windpipe, a conformation like the reed of a hautboy, 
for the modulation of their notes. A tuneful bird is a ven¬ 
triloquist. The seat of the song is in the breast. [PI. 
XXI. fig. 3.] 
The use of the lungs in the system has been said to be 
obscure: one use however is plain, though, in some sense, 
externa] to the system, and that is, the formation, in con¬ 
junction with the larynx, of voice and speech. They are, to 
animal utterance, what the bellows arc to the organ. 
For the sake of method, we have considered animal bo¬ 
dies under three divisions: their bones, their muscles, and 
their vessels; and we have stated our observations upon 
