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the teeth. What they ftood in need of, was a ftrong, hard, infenfible, defensive coat: and exactly fuch a covering is given to them, in the ivory enamel which adheres to their furface.

2. The scarf-fkin, which clothes all the rest of the body, gives way, at the extremities of the toes and fingers, to nails. A man has only to look at his hand, to obferve with what nicety and precision, that covering, which extends over every other part, is here superseded by a different substance and a different texture. Now, if either the rule had been neceffary, or the deviation from it accidental, this effect would not be feen. When I fpeak of the rule being neceffary, I mean the formation of the fkin upon the furface being produced by a set of causes constituted without defign, and acting, as all ignorant causes must act, by a general operation. Were this the cafe, no account could be given of the operation being fufpended at the fingers' ends, or on the back part of the fingers, and not on the fore part. On the other hand; if the deviation were accidental, an error, an anomalifm; were it any thing else than fettled by intention; we should meet with

nails upon other parts of the body. They would be scattered over the surface, like warts or pimples.

3. All the great cavities of the body are inclosed by membranes except the skull. Why fhould not the brain be content with the fame covering as that which ferves for the other principal organs of the body? The heart, the lungs, the liver, the ftomach, the bowels, have all foft integuments, and nothing else. The muscular coats are all foft and membranous. I can fee a reafon for this diftinction in the final cause, but in no other. The importance of the brain to life, (which experience proves to be immediate,) and the extreme tendernefs of its fubftance, make a folid cafe more neceffary for it, than for any other part and such a case the hardness of the skull supplies. When the smallest portion of this natural cafquet is loft, how carefully, yet how imperfectly, is it replaced by a plate of metal? If an anatomist should fay, that this bony protection is not confined to the brain, but is extended along the course of the spine, I answer, that he adds ftrength to the argument. If he remark, that the cheft alfo is fortified by bones, I reply, that I should have alledged this inftance

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ftance myself, if the ribs had not appeared fubfervient to the purpose of motion, as well as of defence. What diftinguishes the skull from every other cavity is, that the bony covering completely furrounds its contents, and is calculated, not for motion, but folely for defence. Those hollows, likewise, and inequalitics, which we obferve in the inside of the skull, and which exactly fit the folds of the brain, answer the important defign of keeping the substance of the brain steady, and of guarding it against concuffions.

CHAP

CHAPTER XII.

COMPARATIVE ANATOMY.

WHENEVER we find a general plan pursued, yet with fuch variations in it, as are, in each cafe, required by the particular exigency of the fubject to which it is applied, we poffefs, in fuch plan and fuch adaptation, the strongest evidence, that can be afforded, of intelligence and defign; and evidence, which the most completely excludes every other hypothefis. If the general plan proceeded from any fixed neceffity in the nature of things, how could it accommodate itself to the various wants and ufes which it had to ferve, under different clrcumftances, and on different occafions? Arkwright's mill was invented for the spinning of cotton. We fee it employed for the spinning of wool, flax, and hemp, with fuch modifications of the original principle, such variety in the fame plan, as the texture of those different materials rendered neceffary. Of the machine's being put together with design,

if it were poffible to doubt, whilft we faw it only under one mode, and in one form; when we came to obferve it in its different applications, with fuch changes of structure, fuch additions, and fupplements, as the special and particular ufe in each cafe demanded, we could not refuse any longer our affent to the propofition, "that intelligence, properly and strictly fo called (including under that name, forefight, confideration, reference to utility,) had been employed, as well in the primitive plan, as in the several changes and accommodations which it is made to undergo."

Very much of this reafoning is applicable to what has been called Comparative Anatomy. In their general economy, in the outlines of the plan, in the construction as well as offices of their principal parts, there exifts, between all large terreftrial animals, a close refemblance. In all, life is fuftained, and the body nourished, by nearly the fame apparatus. The heart, the lungs, the ftomach, the liver, the kidneys, are much alike in all. The same fluid (for no diftinction of blood has been observed) circulates through their vessels, and nearly in the fame order. The same cause,

therefore,

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