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complete, that is, are not cartilaginous and stiff all round; but their hinder parts, 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 fame 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 another 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 convulsed 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 capacity of perceiving with such acuteness; this impatience of offence, yet perfect rest and ease when let alone; are properties, one would have thought, not likely to reside in the fame subject. It is to the junction however of these almost inconsistent qualities, in this.as well as in some other delicate parts of the body, that we owe our fafety and out 'comfort j
comfort; our fasety 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,) beside its other uses, is also a musical instrument, that is to fay, 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 founded,' just as a pipe or flute is founded, 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 ventriloquist. The seat of the song is in the breast.
The use of the lungs in the system has been faid to be obscure: one use however is plain, though, in some sense, external to the system, and that is, the formation, in conjunction with the larynx, of voice and speech. They are, to animal utterance, what the bellows are to the organ.
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For the fake of method, we have considered animal bodies 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 in their separate but their collective action; in their mutual subserviency and dependence; in their contributing together to one effect, and one use. It has been laid, that a man cannot lift his hand to his head wihtout finding enough to convince him of the existence of a God. And it is well faid; for he has only to reflect, familiar as this action is, and simple as it seems to be, how many things are requisite for the performing of it; how many things which we understand, to fay nothing of many more, probably, which we do not; viz. first, a long, hard, strong cylinder, in order to give to the arm its firmness and tension ; but which, being rigid and, in its substance, inflexible, can only turn upon joints: secondly therefore, joints for this purpose, one at the shoulder to raise the arm, another at the elbow to bend it; these joints continually fed with a soft mucilage to make the parts flip easily upon one
another, another, and held together by strong braces to keep them in their position: then, thirdly, strings and wire, i. e. muscles and tendons, artisicia'ly inserted for the purpose of drawing the bones in the directions in which the joints allow them to move. Hitherto ye seem to understand the mechanism pretty well; and understanding this, we possess enough for our conclusion: nevertheless we have hitherto only a machine standing still; a dead organization; an apparatus. To put the system in a state of activity (to set it at work) a further provision is necessary, viz. a communication with the brain by mea^s of nerves. We know the existence of this communication, because we can see the communicating threads, and can trace them to the brain: its necessity we also know, because, if the thread be cut, if the communication be intercepted, the muscle becomes paralytic : but beyond this we know little; the organization being too minute and subtile for our inspection.
To what has been enumerated, as officiating in the single act of a man's raising his hand to his head, must be added likewise, all that is necessary, and all that contributes, to the growth, nourishment, and sustentation of the o 3 limb, limb, the repair of its waste, the preservation of its health: such as the circulation of the blood through every part of it; its lymphatics, exhalants, absorbents; its excretions and integuments. All these share in the result; join in the effect: and how all these, or any of them, come together without a designing, disposing intelligence, it is impossible to conceive.