is an instance upon which I lay my hand. One single fact, weighed by a mind in earnest, leaves oftentimes the deepest impression. For the purpose of addressing different understandings and different apprehensions— for the purpose of sentiment, for the purpose of exciting admiration of the Creator's works, we diversify our views, we multiply our examples; but for the purpose of strict argument, one clear instance is sufficient; and not only sufficient, but capable perhaps of generating a firmer assurance than what can arise from a divided attention.

*

The ginglymus, or hinge-joint, does not, it is manifest, admit of a ligament of the same kind with that of the ball-and-socket joint, but it is always fortified by the species of ligament of which it does admit. The strong, firm, investing membrane, above described, accompanies it in every part and in particular joints, this membrane, which is properly a ligament, is considerably stronger on the sides than either before or behind, in order that the convexities may play true in their concavities, and not be subject to slip sideways, which is the chief danger; for the muscular tendons generally restrain the parts from going farther 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 superadded to the common provisions for the stability of the joint, two strong ligaments which cross each other; and cross each other in such a manner, as to secure the joint from being displaced in any assignable direction. "I think,” says Cheselden, ceros-it is wanting in the Elephant only, whose limbs, ill qualified for active movements, do not seem to require this security to the joint. *The sides of hinge-joints are always strengthened by lateral ligaments, distinct from the capsular, the use of which is correctly stated.

Fig. 2 and 4, the crucial or internal ligaments of the knee-joint, arise from each side of the depression between the condyles of the thigh

"that the knee cannot be completely dislocated without breaking the cross ligaments." We can hardly help comparing this with the binding up of a fracture, where the fillet is almost always strapped across, for the sake of giving firmness and strength to the bandage.

Another no less important joint, and that also of the ginglymus sort, is the ankle; yet though important, (in order, perhaps, to preserve the symmetry and lightness of the limb,) small, and on that account more likely to injury. Now this joint is strengthened, i. e. is defended from dislocation, by two remarkable processes or prolongations of the bones of the leg which processes 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: so that, if the joint be in danger of slipping outward, it is curbed by the inner projection, i. e. that of the tibia; if inward, by the outer projection, i. e. that of the fibula. Between both, it is locked in its position. I know no account that can be given of this structure, except its utility. Why should the tibia terminate, at its lower extremity, with a double end, and the fibula the samebut to barricade the joints on both sides by a continuation of part of the thickest of the bone over it ?* The bone; the anterior is fixed into the centre, the posterior into the back of the articulation of the tibia. This structure properly limits the motions of the joint, and gives the firmness requisite for violent exertions. Viewing the form of the bones, we should consider it one of the weakest and most superficial, but the strength of its ligaments and the tendons passing over it renders it the most secure, and the least liable to dislocation of any joint in the whole body.

*Fig. 4: a, the fibula; b, the tibia, the lower extremities of which, c, d, form the outer and inner ankle, and receive e, the great articulating bone of the foot, called the astragalus, between them. When the foot sustains the weight of the body the joint is firm; but when raised, it easily rolls on the end of these bones, so that the toe is directed to the place on which we intend to step.

joint at the shoulder, compared with the joint at the hip, though both ball-and-socket joints, discovers a difference in their form and proportions, well suited to the different offices which the limbs have to execute. The cup or socket at the shoulder is much shallower and flatter than it is at the hip, and is also in part formed of cartilage set round the rim of the cup. The socket, into which the head of the thigh-bone is inserted, is deeper, and made of more solid materials.* This agrees with the duties assigned to each part. The arm is an instrument of motion, principally, if not solely. Accordingly, the shallowness of the socket at the shoulder, and the yieldingness of the cartilaginous substance with which its edge is set round, and which in fact composes a considerable part of its concavity, are excellently adapted for the allowance of a free motion and a wide range; both which the arm wants. Whereas, the lower limb, forming a part of the column of the body; having to support the body, as well as to be the means of its locomotion; firmness was to be consulted, as well as action. With a capacity for motion, in all directions indeed, as at the shoulder, but not in any direction to the same extent as in the arm, was to be united stability, or resistance to dislocation. Hence the deeper excavation of the socket; and the presence of a less proportion of cartilage upon the edge.

The suppleness and pliability of the joints we every moment experience; and the firmness of animal articulation, the property we have hitherto been considering,

* The socket for the head of the thigh-bone is indeed deeper than that at the shoulder, but the "materials” which form the concavities are the same; both are solid bone covered by cartilages, and both have a rim of a strong fibro-cartilaginous texture, not only for the purpose of rendering the socket deeper, but for preventing fractures of the rim in robust exercises, to which, were it bony, it would be very liable.

may be judged of from this single observation-that, at any given moment of time, there are millions of animal joints in complete repair and use, for one that is dislocated; and this, notwithstanding the contortions and wrenches to which the limbs of animals are continually subject.

II. The joints, or rather the ends of the bones which form them, display also, in their configuration, another use. The nerves, blood-vessels, and tendons, which are necessary to the life, or for the motion of the limbs, must, it is evident, in their way from the trunk of the body to the place of their destination, travel over the moveable joints; and it is no less evident, that, in this part of their course, they will have, from sudden motions, and from abrupt changes of curvature, to encounter the danger of compression, attrition, or laceration. To guard fibres so tender against consequences so injurious, their path is in those parts protected with peculiar care; and that by a provision in the figure of the bones themselves. The nerves which supply the fore-arm, especially the inferior cubital nerves, are at the elbow conducted, by a kind of covered way, between the condyles, or rather under the inner extuberence of the bone which composes the upper part of the arm.* At the knee, the extremity of the thigh-bone is divided by a sinus or cleft into two heads or protuberances : and these heads on the back part stand out beyond the cylinder of the bone. Through the hollow, which lies between the hind-parts of these two heads, that is to say, under the ham, between the hamstrings, and within the concave recess of the bone formed by the extuberences

* In many animals, the nerves of the fore-leg, which correspond with these nerves, for their protection are actually conducted through a hole in the bone.

on each side; in a word, along a defile, between rocks, pass the great vessels and nerves which go to the leg. Who led these vessels by a road so defended and secured? In the joint at the shoulder, in the edge of the cup which receives the head of the bone, is a notch,* which is joined or covered at the top with a ligament. Through this hole, thus guarded, the blood-vessels steal to their destination in the arm, instead of mounting over the edge of the concavity.

III. In all joints, the ends of the bones, which work against each other, are tipped with gristle. In the ball-and-socket joint, the cup is lined, and the ball capped with it. The smooth surface, the elastic and unfriable nature of cartilage, render it of all substances the most proper for the place and purpose. I should, therefore, have pointed this out amongst the foremost of the provisions which have been made in the joints for the facilitating of their action, had it not been alleged, that cartilage in truth is only nascent or imperfect bone; and that the bone in these places is kept soft and imperfect, in consequence of a more complete and rigid ossification being prevented from taking place by the continual motion and rubbing of the surfaces; which being so, what we represent as a designed advantage, is an unavoidable effect. I am far from being convinced that this is a true account of the fact; or that, if it were so, it answers the argument. To me, the surmounting of the ends of the bones with gristle, looks more like a plating with a different metal, than like the same metal, kept in a different state by the action to which it is

* This is called the semilunar notch; it is not "in the edge of the cup," but on the superior border of the bone, and near the cavity; sec a, Tab. X. Fig. 4. A ligament extends from one point of the notch to the other, forming a foramen, which is traversed by the superior scapular nerves and blood-vessels.

VOL. IV.