may be turned upward. How is this managed? The fore-arm, it is well known, consists of two bones, lying alongside each other, but touching only towards the ends. One, and only one, of these bones is joined to the cubit, or upper part of the arm, at the elbow; the other alone to the

[Since it has been our author's pleasure to take this instance, the figure will illustrate his description. A is the lower part of the arm-bone, or humerus; B is the ulna and C the radius, the two bones of the forearm. It will be understood how these bones, being tied together by ligaments, hinge and move upon the humerus A; c being the process of the ulna, on which we rest when leaning on the elbow. By applying our hand to the arm, we at once feel the freedom with which the bone moves in bending and extending the arm.When we turn the key in a lock, or make the guards in fencing by the motion of the wrist, the ulna B is stationary, and the radius C turns round upon the head of the bone at d and e, carrying the hand with it. The rest is abundantly well explained in the text.]

hand at the wrist. The first, by means, at the elbow, of a hinge-joint (which allows only of motion in the same plane), swings backward and forward, carrying along with it the other bone, and the whole fore-arm. In the mean time, as often as there is occasion to turn the palm upward, that other bone to which the hand is attached rolls upon the first, by the help of a groove or hollow near each end of one bone, to which is fitted a corresponding prominence in the other. If both bones had been joined to the cubit, or upper arm, at the elbow, or both to the hand at the wrist, the thing could not have been done. The first was to be at liberty at one end, and the second at the other; by which means the two actions may be performed together. The great bone which carries the fore-arm may be swinging upon its hinge at the elbow, at the very time that the lesser bone, which carries the hand, may be turning round it in the grooves. The manage

ment, also, of these grooves, or rather of the tubercles and grooves, is very observable. The two bones are called the radius and the ulna. Above, i. e., towards the elbow, a tubercle of the radius plays into a socket of the ulna; whilst below, i. e., towards the wrist, the radius finds the socket, and the ulna the tubercle. A single bone in the fore-arm, with a ball-and-socket joint at the

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elbow, which admits of motion in all directions, might, in some degree, have answered the purpose of both moving the arm and turning the hand. But how much better it is accomplished by the present mechanism any person may convince himself who puts the ease and quickness with which he can shake his hand at the wrist circularly (moving likewise, if he pleases, his arm at the elbow at the same time) in competition with the comparatively slow and laborious motion with which his arm can be made to turn round at the shoulder by the aid of a ball and socket joint.

III. The spine, or back-bone, is a chain of joints. of very wonderful construction. Various, difficult, and almost inconsistent offices were to be executed by the same instrument. It was to be firm, yet flexible (now, I know no chain made by art which is both these; for by firmness I mean, not only strength but stability); firm, to support the erect position of the body; flexible, to allow of the bending of the trunk in all degrees of curvature. It was further also (which is another and quite a distinct purpose from the rest) to become a pipe or conduit for the safe conveyance from the brain of the most important fluid of the animal frame, that, namely, upon which all voluntary motion depends, the spinal marrow; a substance not only of the first necessity to action, if not to life, but

of a nature so delicate and tender, so susceptible and so impatient of injury, as that any unusual pressure upon it, or any considerable obstruction of its course, is followed by paralysis or death.

[This represents a section of three of the lower vertebræ. The subject being by no means exhausted in the text, the reader will find it taken up in the Appendix.]

Now the spine was not only to furnish the main trunk for the passage of the medullary substance from the brain, but to give out, in the course of its progress, small pipes therefrom, which, being afterwards indefinitely subdivided, might, under the name of nerves, distribute this exquisite supply to every part of the body. The same spine was also to serve another use not less wanted than

the preceding, viz., to afford a fulcrum, stay, or basis (or, more properly speaking, a series of these) for the insertion of the muscles which are spread over the trunk of the body; in which trunk there are not, as in the limbs, cylindrical bones to which they can be fastened: and likewise, which is a similar use, to furnish a support for the ends of the ribs to rest upon.

Bespeak of a workman a piece of mechanism which shall comprise all these purposes, and let him set about to contrive it; let him try his skill upon it; let him feel the difficulty of accomplishing the task, before he be told how the same thing is effected in the animal frame. Nothing will enable him to judge so well of the wisdom which has been employed; nothing will dispose him to think of it so truly. First, for the firmness, yet flexibility, of the spine; it is composed of a great number of bones (in the human subject, of twentyfour) joined to one another, and compacted by broad bases. The breadth of the bases upon which the parts severally rest, and the closeness of the junction, give to the chain its firmness and stability; the number of parts, and consequent frequency of joints, its flexibility. Which flexibility, we may also observe, varies in different parts of the chain; is least in the back, where strength more than flexure is wanted; greater in the loins,