complete, that is, are not cartilaginous and ftiff all round; but their hinder part, which is contiguous to the gullet, is membranous and foft, eafily yielding to the distensions of that organ occafioned by the defcent of folid food. The fame rings are alfo bevelled off at the upper and lower edges, the better to close upon one another, when the trachea is compreffed or fhortened.

The conftitution of the trachea may fuggeft likewife another reflection. The membrane which lines its infide, is, perhaps, the moft fenfible, irritable, membrane of the body. It rejects the touch of a crumb of bread, or a drop of water, with a fpafm which convulfes the whole frame; yet, left to itself, and its proper office, the intromiffion of air alone, nothing can be fo quiet. It does not even make itself felt: a man does not know that he has a trachea. This capacity of perceiving with fuch acutenefs; this impatience of offence, yet perfect reft and ease when let alone; are properties, one would have thought, not likely to refide in the fame fubject. It is to the junction however of these almoft inconfiftent qualities, in this as well as in fome other delicate parts of the body, that we owe our safety and out comfort;

comfort; our fafety to their fenfibility, our comfort to their repofe.

The larynx, or rather the whole windpipe taken together, (for the larynx is only the upper part of the windpipe,) befide its other uses, is also a musical instrument, that is to fay, it is mechanifm expressly adapted to the modulation of found; 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, juft as a pipe or flute is founded. Birds, fays 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 ventriloquift. The feat of

the fong is in the breast.

The use of the lungs in the system has been. faid to be obfcure: one ufe however is plain, though, in fome sense, external to the fyftem, 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.

For the fake of method, we have confidered animal bodies under three divifions, their bones, their muscles, and their veffels and we have stated our obfervations upon these parts feparately. But this is to diminish the ftrength of the argument. The wisdom of the Creator is feen, not in their separate but their collective action; in their mutual fubferviency and dependence; in their contributing together to one effect, and one ufe. It has been faid, 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 fimple as it feems to be, how many things are requifite 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, ftrong cylinder, in order to give to the arm its firmness and tenfion; but which, being rigid and, in its fubftance, inflexible, can only turn upon joints: fecondly therefore, joints for this purpose, one at the fhoulder 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 pofition: then, thirdly, ftrings and wires, i. e. mufcles and tendons, artificially inferted for the purpose of drawing the bones in the directions in which the joints allow them to move. Hitherto we seem to understand the mechanifin pretty well; and understanding this, we possess enough for our conclufion: nevertheless we have hitherto only a machine standing ftill; a dead organization; an apparatus. To put the fyftem in a state of activity (to fet it at work) a further provision is neceffary, viz. a communication with the brain by means of nerves. We know the existence of this communication, because we can fee the communicating threads, and can trace them to the brain: its neceffity we also know, because, if the thread be cut, if the communication be intercepted, the mufcle becomes paralytic: but beyond this we know little; the organization being too minute and fubtile for our inspection.

To what has been enumerated, as officiating in the fingle a of a man's raising his hand to his head, must be added likewife, all that is neceffary, and all that contributes, to the growth, nourishment, and fuftentation of the limb,

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limb, the repair of its wafte, the preservation of its health: fuch as the circulation of the blood through every part of it; its lymphtics, exhalants, abforbents; its excretions and integuments. All these share in the refult; join in the effect: and how all these, or any of them, come together without a defigning, difpofing intelligence, it is impoffible to conceive.

CHAP