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parts of the body, notches are made in the upper and lower edge of every vertebra; two on each edge; equidistant on each side from the middle line of the back. When the vertebræ are put together, these notches, exactly fitting, form small holes; through which the nerve?, at each articulation, issue out in pairs, in order to send their branches to every part of the body, and with an equal bounty to both sides of the body. The fourth purpose assigned to the fame instrument, is the insertion of the bases of the muscles, and the support of the ends of the ribs: and for this fourth purpose, especially the former part of itj a figure, specifically suited to the design, and unnecessary for the other purposes, is given to the constituent bones. Whilst they are plain, astd' round, and smooth towards the front, where any roughness or projections might have wounded the adjacent viscera, they run our, behind, and on each side, into long processes, to which processes the muscles necessary to the tfiotions of the trunk are fixed; and fixed \tfkhV'luch'-art", that, whilst the vetebræ supply la-"b6ifis-fbr the muscles, the muscles help ttf &eep'these bones in their positiony ©* by their tendons- to tie* them t<s>g«thetv-' , '».»•, j That
That most important, however, and general property, viz. the strength of the compages, and the security against luxation, was to be still more specially consulted; for where so many joints were concerned, and where, in every one, derangement would have been fatal, it became a subject of studious precaution. For this purpose, the vertebrae are articulated, that is, the moveable joints between them are formed, by means of those projections of their substance, which we have mentioned under the -name of processes; and these so lock in with, and overwrap, one another, as to secure the body of the vertebra, not only from accidentally flipping, but even from being pushed, out of its place, by any violence short of that which would break the bone, I have often remarked and admired this structure in the chine of a hare. In this, as in many instances, a plain observer of the animal œconomy may spare himself the disgust of being present at human dissections, and, yet learn enough for his information and fatisfaction, by even examining the bones of the animals which come upon his table. Let him take, for example, into his hands, a piece of the clean-picked bone of a hare's back; consisting, we will suppose of three vertebræ. He will find the middle bone of the three, so Implicated, by means of its projections or processes, with the bone on each side of it, that no pressure which he can use, will force it out of its place between them. It will give way neither forward, nor backward, nor on either side. In whichever direction he pushes, he perceives, in the form, or junction, or overlapping of the bones, an impediment opposed to his attempt; a check and guard against dislocation. In one part of the spine, he will find a still further fortifying expedient, in the mode according to which the ribs are annexed to the spine. Each rib rests upon two vertebræ. That is the thing to be remarked, and any one may remark it in carving a neck of mutton. The manner of it is this: the end of the rib is divided by a middle ridge into two surfaces, which surfaces are joined to the bodies of two contiguous vertebrae, the ridge applying itself to the intervening cartilage. Now this is the very contrivance which is employed in the famous iron bridge at my door at Bishop-Wearmouth; and for the fame purpose of stability; viz. the cheeks of the bars, which pass between the arches, ride
across across the joints, by which the pieces composing each arch are united. Each cross bar rests upon two of these pieces at their place of junction; and by that position resists, at least in one direction, any tendency in either piece to flip out of its place. Thus persectly, by one means or the other, is the danger of flipping laterally, or of being drawn aside out of the line of the back provided against: and, to withstand the bones being pulled asunder longitudinally, or in the direction of the line, a strong membrane runs from one end of the chain to the other, sufficient to resist any force which is ever likely to act in the direction of the back, or parallel to it, and consequently to secure the whole combination in their places. The general result is, that not only the motions of the human body necessary for the ordinary offices of life are performed with safety, but that it is an accident hardly ever heard of, that even the gesticulations of a harlequin distort his spine.
Upon the whole, and as a guide to those who may be inclined to carry the consideration of this subject further, there are three views under which the spine ought to be regarded, and in all which it cannot fail to excite our admiration.
These These views relate to its articulations, its ligaments, and its perforation; and to the corre* sponding advantages which the body derives from it, for action, for strength, and for that, which is essential to every part, a secure communication with the brain.
The structure of the spine is not in" general different in different animals. In the serpent tribe, however, it is considerably varied; but with a strict reference to the convenience of the animal. For, whereas in quadrupeds the number of vertebra is from thirty to forty, in the serpent it is nearly one hundred and fifty: whereas in men and quadrupeds the surfaces of the bones are flat, and these flat surfaces laid one against the other, and bound tight by sinews; in the serpent, the bones play one within another like a ball and socket *, so that they have a free motion upon one another in every direction: that is to fay, in men and quadrupeds firmness is more consulted; in serpents, pliancy. Yet even pliancy is not obtained at the expense of safety. The backbone of a serpent, for coherence and flexM bility, is one of the most curious pieces of
* Der. Phjrs. Theol. p. 396.