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ing upon the smallest base, in man. There 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 secure of standing half an hour. You are obliged to fix its feet to the block by bolts and solder, or the first shake, the fu/t gust of wind, is sure to throw it down. Yet this statue shall 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 sufficient. Either the law of gravitation is suspended in favor of living substances, or something more is done for them, in order to enable them to uphold their posture. There is no reason whatever to doubt, but that their parts descend 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 set, of obscure indeed, but of quick balancing actions, so 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 observed, first, that they in part constitute what we call strength. The dead body drops down. The mere adjustment ment therefore of weight and pressure, which may be the fame the moment after death as the moment before, does not support the column. In cases also of extreme weakness the patient cannot stand upright. Secondly, that these actions are only in a small degree voluntary. A man is seldom conscious 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 so called, links 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 still 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 consessed, difficult to explain. Perhaps the obscure motion of the bones of the seet may have their share in this effect. They are put in action by every flip or vacillation of the body, and seem to assist in restoring its balance. Certain it is, that this 9 _ circumstance
circumstance in the structure of the foot, viz. its being composed of many small bones, applied to, and articulating with, one another, by diversely shaped surfaces, instead of being made of one piece, like the last of a shoe, is very remarkable. I suppose also that it would be difficult to stand firm upon stilts or wooden legs, though their base exactly imitated the figure and dimensions of the sole 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 monent in preserving the equilibrium of the body. With respect to this last circumstance it is observable, that the vertebrae are so confined by ligaments as to allow no more flipping upon their bases, than what is just sufficient to break the shock which any violent motion may occasion to the body. A certain degree also of tension of the sinews appears to be essential to an erect posture; for it is by the loss of this, that the dead or paralytic body drops down. The whole is a wonderful result of combined powers, and of very complicated operations.
We have faid that this property is the most: worthy of observation in the human body: but a bird> resting upon its perch, or hopping upon a spray, affords no mean specimen of the fame faculty. A chicken runs off as soon as it is hatched from the egg; yet a chicken, considered geometrically, and with relation to its centre of gravity, its line of direction, and its equilibrium, is a very irregular solid. Is this gift, therefore, or instruction? May it not be said to be with great attention, that nature hath balanced the body upon its pivots?
I observe also in the fame bird a piece of useful mechanism of this kind. In the trusting 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 rests upon its perch. And in this position it steeps in safety ; for the claws do their office in keeping hold of the support, not by any exertion of voluntary power, which steep might suspend, but by the fraction of the tendons, in consequence 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 necessary. .
VI. Regarding the human body as a mass; regarding the general conformations which obtain in it; regarding also 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 such critical deviations can, by any possible hypothesis, be accounted for, without design.
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 use and propriety of this difference; of the" analogy" being thus " interrupted;" of the rule, which belongs to the conformation of the bones, stopping where it does stop: for, had so exquisitely sensible a membrane as the periosteum, invested the teeth, as it invests every other bone of the body, their action, necessary exposure, and irritation, * would have subjected the animal to continual pain. General as it is, it was not the fort of integument which suited