folder, or the first shake, the first guft of wind, is fure to throw it down. Yet this ftatue fhall exprefs all the mechanical proportions of a living model. It is not therefore the mere figure, or merely placing the centre of gravity within the bafe, that is fufficient. Either the law of gravitation is fufpended in favor of living fubftances, or fomething more is done for them, in order to enable them to uphold their pofture. There is no reason whatever to doubt, but that their parts defcend by gravitation in the fame manner as those of dead matter. The gift therefore appears to me to consist in a faculty of perpetually shifting the centre of gravity, by a fet, of obfcure indeed, but of quick balancing actions, fo as to keep the line of direction, which is a line drawn from that centre to the ground, within its preferibed limits. Of thefe actions it may be observed, firft, that they in part conftitute what we call ftrength. The dead body drops down. The mere adjustment therefore of weight and preffure, which may be the fame the moment after death as the moment before, does not support the column. In cafes alfo of extreme weakne's the patient cannot stand upright. Secondly, that thefe actions are only in a fall degree voluntary. A man is feldom confcious of his voluntary powers in keeping himfelt upon his legs. A child learning to walk is the greateft pofture-mafter in the world: but art, if it may be fo called, finks into habit; and he is foon able to poife himself in a great variety of attitudes without being fenfible either of caution or effort.But ftill there must be an aptitude of parts upon which habit can thus attach; a previous capacity of motions which the animal is thus taught to exercise ; and the facility, with which this exercise is acquired, forms one object of our admiration. What parts are principally employed, or in what manner each contributes its office, is, as hath already been confeffed,

difficult to explain. Perhaps the obfcure motion of the bones of the feet may have their share in this effect. They are put in action by every flip or vacillation of the body, and feem to affift in reftoring its balance. Certain it is, that this circumstance in the ftructure of the foot, viz. its being compofed of many small bones, applied to, and articulating with, one another, by diverfely shaped furfaces, instead of being made of one piece, like the laft of a fhoe, is very remarkable. I fuppofe also that it would be difficult to ftand firm upon itilts or wooden legs, though their bafe exactly imitated the figure and dimenfions of the fole of the foot. The alternation of the joints, the knee joint bending backward, the hip joint forward; the flexibility, in every direction, of the spine, especially in the loins and neck, appear to be of great moment in preferving the equilibrium of the body. With respect to this laft circumftance, it is obfervable, that the vertebræ are fo confined by ligaments as to allow no more flipping upon their bafes, than what is juft fufficient to break the fhock which any violent motion may occafion to the body. A certain degree alfo of tenfion of the finews appears to be effential to an erect posture; for it is by the lofs of this, that the dead or paralytic body drops down. The whole is a wonderful refult of combined powers, and of very complicated operations.

We have faid that this property is the moft worthy of observation in the human body: but a bird, refting upon its perch, or hopping upon a spray, affords no mean fpecimen of the fame faculty. A chicken runs off as foon as it is hatched from the egg yet a chicken, confidered geometrically, and with relation to its centre of gravity, its line of direction, and its equilibrium, is a very irregular folid. Is this gift, therefore, or inftruction? May it not be faid to be with great attention, that nature hath balanced the body upon its pivots ?

I observe alfo in the fame bird, a piece of useful mechanifm of this kind. In the truffing of a fowl, upon bending the legs and thighs up towards the body, the cook finds that the claws clofe of their own accord. Now let it be remembered, that this is the pofition of the limbs, in which the bird refts upon its perch. And in this pofition it fleeps in fafety; for the claws do their office in keeping hold of the fupport, not by any exertion of voluntary power, which fleep might fufpend, but by the traction of the tendons, in confequence of the attitude which the legs. and thighs take by the bird fitting down, and to which the mere weight of the body gives the force that is neceffary.

VI. Regarding the human body as a mafs; regarding the general conformations which obtain in it; regarding allo particular parts in refpect to those conformations; we fhall be led to obferve what I call "interrupted analogies." The following are examples of what I mean by these terms: and I don't know how fuch critical deviations can, by any poffible hypothefis, be accounted for, without defign.

1. All the bones of the body are covered with a periofteum, except the teeth, where it ceafes, and an enamel of ivory, which faws and files will hardly touch, comes into its place. No one can doubt of the use and propriety of this difference; of the “analogy" being thus "interrupted;" of the rule, which belongs to the conformation of the bones, ftopping where it does stop: for, had fo exquifitely fenfible a membrane as the periosteum, invefted the teeth, as it invests every other bone of the body, their action, neceflary expofure, and irritation, would have fubjected the animal to continual pain. General as it is, it was not the fort of integument which fuited the teeth. What they flood in need of, was a ftrong, hard, insensible, defenfive coat: and exactly such a

covering is given to them, in the ivory enamel which adheres to their surface.

2. The scarf-fkin, which clothes all the reft 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 precifion, that covering, which extends over every other part, is here fuperfeded by a different fubftance and a different texture. Now, if either the rule had been neceffary, or the deviation from it accidental, this effect would not be seen. When I fpeak of the rule being neceffary, I mean the formation of the skin upon the furface being produced by a fet of caufes conftituted without defign, and acting, as all ignorant caufes 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 settled 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 inclofed 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 elfe. The muscular coats are all soft and membranous. I can fee a reason for this distinction in the final cause, but in no other. The importance of the brain to life, (which experience proves to be immediate,) and the extreme tenderness of its substance, make a folid cafe more necessary for it, than for any other part: and fuch a cafe the hardness of the skull fupplies. 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 anatomift fhould fay, that this bony protection is not confined to the brain, but is extended along the course of the fpine, I anfwer, 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 myfelf, if the ribs had not appeared fubfervient to the purpose of motion, as well as of defence. What distinguishes the fkull 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 likewife and inequalities, which we obferve in the infide of the skull, and which exactly fit the folds of the brain, answer the important defign of keeping the fubftance of the brain steady, and of guarding it against concuffions.

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 subject to which it is applied, we poffefs, in fuch plan and fuch adaptation, the ftrongeft evidence, that can be afforded, of intelligence and defign; and evidence, which the moft completely excludes every other hypothesis. 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 circumftances, and on different occafions? Arkwright's mill was invented for the fpinning of cotton. We fee it employed for the fpin- « ning of wool, flax, and hemp, with such modifications