no use that we know of, in being able to turn the calves of the legs before; and there would have been great confinement by restraining the motion of the thighs to one plane. The difadvantage would not have been lefs, if the joints at the hip and the knee had been both of the fame fort; both balls and fockets, or both hinges: yet why, independently of utility, and of a Creator who confulted that utility, fhould the fame bone (the thigh-bone) be rounded at one end, and channelled at the other?

The hinge joint is not formed by a bolt paffing through the two parts of the hinge, and thus keeping them in their places; but by a different expedient. A ftrong, tough, parchment-like membrane, rifing from the receiving bones, and inferted all round the received bones a little below their heads, incloses the joint on every fide. This membrane ties, confines, and holds the ends of the bones together; keeping the correfponding parts of the joint, i. e. the relative convexities and concavities, in clofe application to each other.

For the ball and focket joint, befide the membrane already defcribed, there is in fome important joints, as an additional security, a short,

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fhort, ftrong, yet flexible ligament, inferted, by one end into the head of the ball, by the other into the bottom of the cup; which ligament keeps the two parts of the joint fo firmly in their place, that none of the motions which the limb naturally performs, none of the jerks and twifts to which it is ordinarily liable, nothing lefs indeed than the utmost and the most unnatural violence, can pull them afunder. It is hardly indeed imaginable, how great a force is neceffary, even to ftretch, fill more to break, this ligament; yet fo flexible is it, as to oppofe no impediment to the fuppleness of the joint. By its fituation. also, it is inacceffible to injury from sharp edges. As it cannot be ruptured, such is its ftrength; fo it cannot be cut, except by an accident which would fever the limb. If I had been permitted to frame a proof of contrivance, fuch as might fatisfy the most diftruftful enquirer, I know not whether I could have chofen an example of mechanifm more unequivocal, or more free from objection, than this ligament. Nothing can be more mechanical; nothing, however fubfervient to the fafety, lefs capable of being generated

by

by the action of the joint. I would particularly folicit the reader's attention to this provifion, as it is found in the head of the thigh-bone; to its ftrength, its ftructure, and its use. It is an inftance upon which I lay my hand. One fingle fact, weighed by a inind in earnest, leaves oftentimes the deepest impreffion. For the purpose of addreffing different understandings and different apprehenfions, for the purpose of fentiment, for the purpose of exciting admiration of the Creator's works, we diverfify our views, we multiply examples; but, for the purpose of ftrict argument, one clear inftance is fufficient: and not only fufficient, but capable perhaps of generating a firmer affurance than what can arife from a divided attention.

The ginglymus, or hinge joint, does not, it is manifeft, admit of a ligament of the fame kind with that of the ball and focket joint, but it is always fortified by the fpecies. of ligament of which it does admit. The ftrong, firm, invefting membrane above defcribed, accompanies it in every part: and, in particular joints, this membrane, which is properly a ligament, is confiderably stronger on the fides than either before or behind, in order

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order that the convexities may play true in their concavities, and not be fubject to slip fideways, which is the chief danger; for the muscular tendons generally reftrain the parts from going further than they ought to go in the plane of their motion. In the knee, which is a joint of this form, and of great importance, there are fuperadded to the common provisions for the ftability of the joint, two ftrong ligaments which crofs each other and crofs each other in fuch a manner, as to fecure the joint from being difplaced in any affignable direction. "I think," fays Chefelden, "that the knee cannot be completely diflocated without breaking the cross ligaments *." We can hardly help comparing this with the binding up of a fracture, where the fillet is alinoft always ftrapped across, for the fake of giving firmness and ftrength to the bandage.

Another no lefs important joint, and that alfo of the ginglymus fort, is the ankle; yet, though important, (in order, perhaps, to preferve the fymmetry and lightnefs of the limb,) fmall, and, on that account, more liable to injury. Now this joint is ftrengthened, i. e.

* Chef. Anat. ed. 7th, p. 45.

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is defended f.om diflocation, by two remarkable proceffes or prolongations of the bones of the leg, which proceffes form the protuberances that we call the inner and outer ankle. It is part of each bone going down lower than the other part, and thereby overlapping the joint: fo that, if the joint be in danger of flipping outward, it is curbed by the inner projection, i. e. that of the tibia ; if inward, by the outer production, i. e. that of the fibula. Between both, it is locked in its pofition. I know no account that can be given of this structure except its utility. Why fhould the tibia terminate, at its lower extremity, with a double end, and the fibula the fame, but to barricade the joint on both fides by a continuation of part of the thickness of the bone over it?

The joint at the shoulder compared with the joint at the hip, though both ball and focket joints, discover a difference in their form and proportions, well fuited to the different offices which the limbs have to execute. The cup or focket at the fhoulder is mu h fhallower and flatter than it is at the hip, and is alfo in part formed of cartilage fet round the rim of the cup. The focket, into which

the