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ing upon the smallest base, in man.

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is more, I think, in the matter than we are aware of. The statue of a man, placed loose upon its pedestal, would not be fecure of ftanding half an hour. You are obliged to fix its feet to the block by bolts and folder, or the first shake, the first guft of wind, is sure to throw it down. Yet this ftatue fhall express all the mechanical proportions of a living model. It is not therefore the mere figure, or merely placing the centre of gravity within the base, that is fufficient. Either the law of gravitation is fufpended in favor of living subftances, 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 thofe of dead matter. The gift therefore appears to me to confist 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 prescribed limits. Of these actions it may be obferved, firft, that they in part conftitute what we call strength. The dead body drops down. The mere adjust

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ment therefore of weight and preffure, which may be the fame the moment after death as the moment before, does not fupport the column. In cafes alfo of extreme weakness the patient cannot stand upright. Secondly, that these actions are only in a small degree voluntary. A man is feldom confcious of his voluntary powers in keeping himself upon his legs. A child learning to walk is the greatest posture-master in the world: but art, if it may be fo called, finks into habit; and he is soon able to poise himself in a great variety of attitudes, without being sensible 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 exercife: and the facility, with which this exercife 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 obscure motion of the bones of the feet may have their fhare in this effect. They are put in action by every flip or vacillation of the body, and feem to affist in reftoring its balance. Certain it is, that this

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circumstance in the ftructure of the foot, viz. its being composed of many small bones, applied to, and articulating with, one another, by diversely shaped furfaces, inftead of being made of one piece, like the laft of a shoe, is very remarkable. I fuppofe alfo that it would be difficult to ftand firm upon ftilts or wooden legs, though their base 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 fpine, especially in the loins and neck, appear to be of great monent in preserving the equilibrium of the body. With refpect to this last circumstance 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

We have faid that this property is the moft worthy of obfervation 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 obferve alfo in the fame bird a piece of ufeful 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 close of their own accord. Now let it be remembered, that this is the position of the limbs, in which the bird refts upon its perch. And in this position it fleeps in safety; 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 mass; regarding the general conformations which obtain in it; regarding alfo particular parts in respect to those conformations; we shall be led to observe 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.

I. All the bones of the body are covered with a periosteum, except the teeth; where it ceases, and an enamel of ivory, which faws and files will hardly touch, comes into its place. No one can doubt of the ufe 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 ftop: for, had fo exquifitely fenfible a membrane as the periosteum, invefted the teeth, as it invests every other bone of the body, their action, neceffary 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

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