108 OF THE VESSELS 



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 wind-pipe taken together, 

 (for the larynx is only the upper part of the wind-pipe,) 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 

 wind-pipe, 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 wind-pipe, 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, 

 external 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 are 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 

 these parts separately. But this is to diminish the strength 

 of the argument. The wisdom of the Creator is seen, not 



