part is not so constructed as to effectuate its purpose whilst it operates according to these laws; but it is because these laws themselves are not in all cases equally understood; or, what amounts to nearly the same thing, are not equally exemplified in more simple processes, and more simple machines; that we lay down the distinction, here proposed, between the mechanical parts and other parts of animals and vegetables.

know perhaps as little as we do of the nervous fluid. But, magnetic attraction being assumed (it signifies nothing from what cause it proceeds.) we can trace, or there can be inted out to us, with perfect clearness and certainty, the mechanism, viz. the steel bars, the wheels, the joints, the wires, by which the motion so much admired is communicated to the fingers of the image: and to make any obscurity, or difficulty, or controverFor instance: The principle of muscular mo- sy, in the doctrine of magnetism, an objection to tion, viz. upon what cause the swelling of the our knowledge or our certainty concerning the belly of the muscle, and consequent contraction of contrivance, or the marks of contrivance, displayed its tendons, either by an act of the will, or by in the automaton, would be exactly the same involuntary irritation, depends, is wholly un- thing, as it is to make our ignorance (which we known to us. The substance employed, whether acknowledge) of the cause of nervous agency, or it be fluid, gaseous, elastic, electrical, or none of even of the substance and structure of the nerves these, or nothing resembling these, is also un- themselves, a ground of question or suspicion as known to us: of course the laws belonging to to the reasoning which we institute concerning that substance, and which regulate its action, are the mechanical part of our frame. That an aniunknown to us. We see nothing similar to this mal is a machine, is a proposition neither correctcontraction in any machine which we can make, ly true nor wholly false. The distinction which or any process which we can execute. So far (it we have been discussing will serve to show how is confessed) we are in ignorance, but no farther. far the comparison, which this expression implies, This power and principle, from whatever cause it holds; and wherein it fails. And whether the proceeds, being assumed, the collocation of the distinction be thought of importance or not, it is fibres to receive the principle, the disposition of certainly of importance to remember, that there is the muscles for the use and application of the neither truth nor justice in endeavouring to bring power, is mechanical; and is as intelligible as the a cloud over our understandings, or a distrust into adjustment of the wires and strings, by which a our reasonings upon this subject, by suggesting puppet is moved. We see, therefore, as far as that we know nothing of voluntary motion, of irrirespects the subject before us, what is not mecha-tability, of the principle of life, of sensation, of nical in the animal frame, and what is. The animal heat, upon all which the animal functions nervous influence (for we are often obliged to give depend; for, our ignorance of these parts of the names to things which we know little about)-I animal frame concerns not at all our knowledge of say the nervous influence, by which the belly, or the mechanical parts of the same frame. I conmiddle, of the muscle is swelled, is not mechani- tend, therefore, that there is mechanism in anical. The utility of the effect we perceive; the mals; that this mechanism is as properly such, means, or the preparation of means, by which it as it is in machines made by art; that this me is produced, we do not. But obscurity as to the chanism is intelligible and certain; that it is not origin of muscular motion, brings no doubtfulness the less so, because it often begins or terminates into our observations upon the sequel of the pro- with something which is not mechanical; that cess: which observations relate, 1st, To the con- whenever it is intelligible and certain, it demonstitution of the muscle; in consequence of which strates intention and contrivance, as well in the constitution, the swelling of the belly or middle works of nature as in those of art; and that it is part is necessarily and mechanically followed by the best demonstration which either can afford. the contraction of the tendons: 2dly, To the number and variety of the muscles, and the corresponding number and variety of useful powers which they supply to the animal; which is astonishingly great: 3dly, To the judicious (if we may be permitted to use that term, in speaking of the Author, or of the works, of nature,) to the wise and well-contrived disposition of each muscle for its specific purpose: for moving the joint this way, and that way, and the other way; for pulling and drawing the part to which it is attached, in a determinate and particular direction; which is a mechanical operation, exemplified in a multitude of instances. To mention only one: The tendon of the trochlear muscle of the eye, to the end that it may draw in the line required, is passed through a cartilaginous ring, at which it is reverted, exactly in the same manner as a rope in a ship is carried over a block or round a stay, in order to make it pull in the direction which is wanted. All this, as we have said, is mechanical; and is as accessible to inspection, as capable of being ascertained, as the mechanism of the automaton in the Strand. Suppose the automaton to be put in motion by a magnet (which is probable,) it will supply us with a comparison very apt for our present purpose. Of the magnetic effluvium, we

But whilst I contend for these propositions, I do not exclude myself from asserting, that there may be, and that there are, other cases, in which, although we cannot exhibit mechanism, or prove indeed that mechanism is employed, we want not sufficient evidence to conduct us to the same conclusion.

There is what may be called the chymical part of our frame; of which, by reason of the imperfection of our chymistry, we can attain to no distinct knowledge; I mean, not to a knowledge, either in degree or kind, similar to that which we possess of the mechanical part of our frame. It does not, therefore, afford the same species of argument as that which mechanism affords; and yet it may afford an argument in a high degree satisfactory. The gastric juice, or the liquor which digests the food in the stomachs of animals, is of this class. Of all menstrua, it is the most active, the most universal. In the human stomach, for instance, consider what a variety of strange substances, and how widely different from one another, it, in a few hours, reduces to a uniform pulp, milk, or mucilage. It seizes upon every thing, it dissolves the texture of almost every thing that comes in its way. The flesh of perhaps all animals; the seeds and fruits of the greatest number of plants; the

roots, and stalks, and leaves, of many, hard and tough as they are, yield to its powerful pervasion. The change wrought by it is different from any chymical solution which we can produce, or with which we are acquainted, in this respect as well as many others, that, in our chymistry, particular menstrua act only upon particular substances. Consider moreover, that this fluid, stronger in its operation than a caustic alkali or mineral acid, than red precipitate, or aqua-fortis itself, is nevertheless as mild, and bland, and inoffensive to the touch or taste, as saliva or gum-water, which it much resembles. Consider, I say, these several properties of the digestive organ, and of the juice with which it is supplied, or rather with which it is made to supply itself, and you will confess it to be entitled to a name, which it has sometimes received, that of "the chymical wonder of animal nature."

Still we are ignorant of the composition of this fluid, and of the mode of its action; by which is meant, that we are not capable, as we are in the mechanical part of our frame, of collating it with the operations of art. And this I call the imperfection of our chymistry; for, should the time ever arrive, which is not perhaps to be despaired of, when we can compound ingredients, so as to form a solvent which will act in the manner in which the gastric juice acts, we may be able to ascertain the chymical principles upon which its efficacy depends, as well as from what part, and by what concoction, in the human body, these principles are generated and derived.

In the mean time, ought that, which is in truth the defect of our chymistry, to hinder us from acquiescing in the inference, which a production of nature, by its place, its properties, its action, its surprising efficacy, its invaluable use, authorises us to draw in respect of a creative design?

lation, by which one and the same blood is converted into bone, muscular flesh, nerves, membranes, tendons; things as different as the wood and iron, canvass and cordage, of which a ship with its furniture is composed. We have no operation of art wherewith exactly to compare all this, for no other reason perhaps than that all operations of art are exceeded by it. No chymical election, no chymical analysis or resolution of a substance into its constituent parts, no mechanical sifting or division, that we are acquainted with, in perfection or variety, come up to animal secretion. Nevertheless, the apparatus and process are obscure; not to say absolutely concealed from our inquiries. In a few, and only a few instances, we can discern a little of the constitution of a gland. In the kidneys of large animals, we can trace the emulgent artery dividing itself into an infinite number of branches; their extremities every where communicating with little round bodies, in the substance of which bodies the secret of the machinery seems to reside, for there the change is made. We can discern pipes laid from these round bodies toward the pelvis, which is a basin within the solid of the kidney. We can discern these pipes joining and collecting together into larger pipes; and, when so collected, ending in innumerable papillæ, through which the secreted fluid is continually oozing into its receptacle. This is all we know of the mechanism of a gland, even in the case in which it seems most capable of being investigated. Yet to pronounce that we know nothing of animal secretion, or nothing satisfactorily, and with that concise remark to dismiss the article from our argument, would be to dispose of the subject very hastily and very irrationally. For the purpose which we want, that of evincing intention, we know a great deal. And Another most subtile and curious function of what we know is this. We see the blood carried animal bodies is secretion. This function is semi- by a pipe, conduit, or duct, to the gland. We see chymical and semi-mechanical; exceedingly im- an organized apparatus, be its construction or portant and diversified in its effects, but obscure action what it will, which we call that gland. We in its process and in its apparatus. The import- see the blood, or part of the blood, after it has ance of the secretory organs is but too well attest- passed through and undergone the action of the ed by the diseases, which an excessive, a deficient, gland, coming from it by an emulgent vein or or a vitiated secretion is almost sure of producing artery, i. e. by another pipe or conduit. And we A single secretion being wrong, is enough to see also at the same time a new and specific fluid make life miserable, or sometimes to destroy it. issuing from the same gland by its excretory duct, Nor is the variety less than the importance. From i. e. by a third pipe or conduit; which new fluid one and the same blood (I speak of the human is in some cases discharged out of the body, in body) about twenty different fluids are separated; more cases retained within it, and there executin their sensible properties, in taste, smell, colour, ing some important and intelligent office. Now and consistency, the most unlike one another that supposing, or admitting, that we know nothing of is possible; thick, thin, salt, bitter, sweet; and, if the proper internal constitution of a gland, or of from our own we pass to other species of animals, the mode of its acting upon the blood; then our we find amongst their secretions not only the most situation is precisely like that of an unmechanical various, but the most opposite properties; the most looker on, who stands by a stocking-loom, a cornnutritious aliment, the deadliest poison; the sweet- mill, a carding machine, or a thrashing-machine, at est perfumes, the most fœtid odours. Of these work, the fabric and mechanism of which, as well the greater part, as the gastric juice, the saliva, as all that passes within, is hidden from his sight the bile, the slippery mucilage which lubricates by the outside case; or, if seen, would be too comthe joints, the tears which moisten the eye, the plicated for his uninformed, uninstructed underwax which defends the ear, are, after they are standing to comprehend. And what is that situasecreted, made use of in the animal economy; are tion? This spectator, ignorant as he is, sees at evidently subservient, and are actually contribut- one end a material enter the machine, as uning to the utilities of the animal itself. Other ground grain the mill, raw cotton the cardingfluids seem to be separated only to be rejected. machine, sheaves of unthrashed corn the thrashThat this also is necessary (though why it was ing-machine; and, when he casts his eye to the originally necessary, we cannot tell,) is shown by other end of the apparatus, he sees the material the consequence of the separation being long sus-issuing from it in a new state; and, what is more, pended; which consequence is disease and death. in a state manifestly adapted to future uses; the Akin to secretion, if not the same thing, is assimi-grain in meal fit for the making of bread, the wool

Of the Bones.

in rovings ready for spinning into threads, the | as, amongst those which have come to our knowsheaf in corn dressed for the mill. Is it necessary ledge, appear to be the most striking, and the best that this man, in order to be convinced that de- understood; but obliged, perhaps, to postpone both sign, that intention, that contrivance, has been these recommendations to a third; that of the exemployed about the machine, should be allowed ample being capable of explanation without plates, to pull it to pieces; should be enabled to examine or figures, or technical language. the parts separately; explore their action upon one another, or their operation, whether simultaneous or successive, upon the material presented to them? He may long to do this to gratify his curiosity; he may desire to do it to improve his theoretic knowledge; or he may have a more substantial reason for requesting it, if he happen, instead of a common visitor, to be a millwright by profession, or a person sometimes called in to repair such-like machines when out of order; but, for the purpose of ascertaining the existence of counsel and design in the formation of the machine, he wants no such intromission or privity. What he sees, is sufficient. The effect upon the material, the change produced in it, the utility of that change for future applications, abundantly testify, be the concealed part of the machine or of its construction what it will, the hand and agency of a contriver.

I-I challenge any man to produce, in the joints and pivots of the most complicated or the most flexible machine that was ever contrived, a construction more artificial, or more evidently artificial than that which is seen in the verte bræ of the human neck.-Two things were to be done. The head was to have the power of bending forward and backward, as in the act of nodding, stooping, looking upward or downward; and, at the same time, of turning itself round upon the body to a certain extent, the quadrant we will say, or rather, perhaps, a hundred and twenty degrees of a circle. For these two purposes, two distinct contrivances are employed: First, the head rests immediately upon the uppermost of the vertebræ, and is united to it If any confirmation were wanting to the evi- by a hinge-joint; upon which joint the head plays dence which the animal secretions afford of design, freely forward and backward, as far either way as it may be derived, as has been already hinted, is necessary, or as the ligaments allow: which from their variety, and from their appropriation to was the first thing required. But then the rotatotheir place and use. They all come from the same ry motion is unprovided for; Therefore, secondly, blood: they are all drawn off by glands: yet the to make the head capable of this, a farther meproduce is very different, and the difference ex- chanism is introduced; not between the head and actly adapted to the work which is to be done, or the uppermost bone of the neck, where the hinge the end to be answered. No account can be given is, but between that bone, and the bone next unof this, without resorting to appointment. Why, derneath it. It is a mechanism resembling a tefor instance, is the saliva, which is diffused over non and mortice. This second, or uppermost the seat of taste, insipid, whilst so many others of bone but one, has what anatomists call a process, the secretions, the urine, the tears, and the sweat, viz. a projection, somewhat similar, in size and are salt? Why does the gland within the ear se- shape, to a tooth; which tooth, entering a corresparate a viscid substance, which defends that pas-ponding hole or socket in the bone above it, forms sage; the gland in the upper angle of the eye, a thin brine which washes the ball? Why is the synovia of the joints mucilaginous; the bile bitter, stimulating, and soapy? Why does the juice, which flows into the stomach, contain powers, which make that bowel the great laboratory, as it is by its situation the recipient, of the materials of future nutrition? These are all fair questions; and no answer can be given to them but what calls in intelligence and intention.

My object in the present chapter has been to teach three things: first, that it is a mistake to suppose that, in reasoning from the appearances of nature, the imperfection of our knowledge proportionably affects the certainty of our conclusion; for in many cases it does not affect it at all: secondly, that the different parts of the animal frame may be classed and distributed, according to the degree of exactness with which we can compare them with works of art: thirdly, that the mechanical parts of our frame, or those in which this comparison is most complete, although constituting, probably, the coarsest portions of nature's workmanship, are the most proper to be alleged as proofs and specimens of design.

CHAPTER VIII.

Of Mechanical Arrangement in the Human
Frame.

WE proceed, therefore, to propose certain examles taken out of this class: making choice of such

a pivot or axle, upon which that upper bone, together with the head which it supports, turns freely in a circle; and as far in the circle as the attached muscles permit the head to turn. Thus are both motions perfect, without interfering with each other. When we nod the head, we use the hinge-joint, which lies between the head and the first bone of the neck. When we turn the head round, we use the tenon and mortice, which runs between the first bone of the neck and the second We see the same contrivance and the same principle employed in the frame or mounting of a telescope. It is occasionally requisite, that the objectend of the instrument be moved up and down, as well as horizontally or equatorially. For the vertical motion, there is a hinge, upon which the telescope plays; for the horizontal or equatorial motion, an axis upon which the telescope and the hinge turn round together. And this is exactly the mechanism which is applied to the motion of the head: nor will any one here doubt of the existence of counsel and design, except it be by that debility of mind, which can trust to its own reasonings in nothing.

We may add, that it was on another account also, expedient, that the motion of the head backward and forward should be performed upon the upper surface of the first vertebræ: for if the first vertebræ itself had bent forward, it would have brought the spinal marrow, at the very beginning of its course, upon the point of the tooth.

II. Another mechanical contrivance, not unlike the last in its object, but different and original in

!

its means, is seen in what anatomists call the fore- death. Now the spine was not only to furnish arm; that is, in the arm between the elbow and the main trunk for the passage of the medullary the wrist. Here, for the perfect use of the limb, substance from the brain, but to give out, in the two motions are wanted: a motion at the elbow course of its progress, small pipes therefrom, which backward and forward, which is called a recipro- being afterward indefinitely subdivided, might, cal motion; and a rotatory motion, by which the under the name of nerves, distribute this exquisite palm of the hand, as occasion requires, may be supply to every part of the body. The same turned upward. How is this managed? the fore- spine was also to serve another use not less arm, it is well known, consists of two bones, lying wanted than the preceding, viz. to afford a fulcrum, along-side each other, but touching only towards stay, or basis (or more properly speaking, a series the ends. One, and only one, of these bones, is of these,) for the insertion of the muscles which joined to the cubit, or upper part of the arm at are spread over the trunk of the body: in which the elbow; the other alone, to the hand at the trunk there are not, as in the limbs, cylindrical wrist. The first, by means, at the elbow, of a bones to which they can be fastened: and, likewise, hinge-joint (which allows only of motion in the which is a similar use, to furnish a support for the same plane,) swings backward and forward, car-ends of the ribs to rest upon. rying along with it the other bone, and the whole Bespeak of a workman a piece of mechanism fore-arm. In the mean time, as often as there is which shall comprise all these purposes, and let occasion to turn the palm upward, that other bone him set about to contrive it let him try his skill to which the hand is attached, rolls upon the first, upon it; let him feel the difficulty of accomplishby the help of a groove or hollow near each ending the task, before he be told how the same thing of one bone, to which is fitted a corresponding is effected in the animal frame. Nothing will prominence in the other. If both bones had been enable him to judge so well of the wisdom which joined to the cubit or upper arm, at the elbow, or has been employed; nothing will dispose him to both to the hand at the wrist, the thing could not think of it so truly. First, for the firmness, yet have been done. The first was to be at liberty flexibility, of the spine; it is composed of a great at one end, and the second at the other; by which number of bones (in the human subject, of twenmeans the two actions may be performed together. ty-four) joined to one another, and compacted by The great bone which carries the fore-arm, may broad bases. The breadth of the bases upon be swinging upon its hinge at the elbow, at the which the parts severally rest, and the closeness very time that the lesser bone, which carries the of the junction, give to the chain its firmness and hand, may be turning round it in the grooves. stability; the number of parts, and consequent freThe management also of these grooves, or rather quency of joints, its flexibility. Which flexibility, the tubercles and grooves, is very observable. The we may also observe, varies in different parts of two bones are called the radius and the ulna. the chain; is least in the back, where strength Above, i. e. towards the elbow, a tubercle of the more than flexure is wanted; greater in the loins, radius plays into the socket of the ulna; whilst which it was necessary should be more supple below, i. e. towards the wrist, the radius finds the than the back; and greatest of all in the neck, for socket, and the ulna the tubercle. A single bone the free motion of the head. Then, secondly, in in the fore-arm, with a ball and socket joint at the order to afford a passage for the descent of the elbow, which admits of motion in all directions, medullary substance, each of these bones is bored might, in some degree, have answered the purpose through in the middle in such a manner, as that, of both moving the arm and turning the hand. when put together, the hole in one bone falls into But how much better it is accomplished by the a line, and corresponds with the holes in the two present mechanism, any person may convince bones contiguous to it. By which means, the himself who puts the ease and quickness with perforated pieces, when joined, form an entire, which he can shake his hand at the wrist circu- close, uninterrupted channel; at least, whilst the larly (moving likewise, if he pleases, his arm at spine is upright, and at rest. But as a settled the elbow at the same time,) in competition with posture is inconsistent with its use, a great diffithe comparatively slow and laborious motion, with culty still remained, which was to prevent the which his arm can be made to turn round at the vertebræ shifting upon one another, so as to break shoulder, by the aid of a ball and socket joint. the line of the canal as often as the body moves or twists; or the joints gaping externally, whenever the body is bent forward, and the spine thereupon made to take the form of a bow. These dangers, which are mechanical, are mechanically provided against. The vertebræ, by means of their processes and projections, and of the articulations which some of these form with one another at their extremities, are so locked in and confined, as to maintain, in what are called the bodies or broad surfaces of the bones, the relative position nearly unaltered; and to throw the change and the pressure, produced by flexion, almost entirely upon the intervening cartilages, the springiness and yielding nature of whose substance admits of all the motion which is necessary to be performed upon them, without any chasms being produced by a separation of the parts. I say, of all the motion which is necessary; for although we bend our backs to every degree almost of inclination, the motion of each vertebra is very smail: such is

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 farther 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

the advantage we receive from the chain being composed of so many links, the spine of so many bones. Had it consisted of three or four bones only; in bending the body, the spinal marrow must have been bruised at every angle. The reader need not be told, that these intervening cartilages are gristles; and he may see them in perfection in a loin of veal. Their form also favours the same intention. They are thicker before than behind; so that, when we stoop forward, the compressible substance of the cartilage, yielding in its thicker and interior part to the force which squeezes it, brings the surfaces of the adjoining vertebræ nearer to the being parallel with one another than they were before, instead of increas-ridge into two surfaces; which surfaces are joined ing the inclination of their planes, which must have occasioned a fissure or opening between them. Thirdly, for the medullary canal giving out in its course, and in a convenient order a supply of nerves to different parts of the body, notches are made in the upper and lower edge of every vertebra; two on each edge; equi-distant 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 nerves, 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 same 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 it, a figure, specifically suited to the design, and unnecessary for the other purposes, is given to the constituent bones. Whilst they are plain, and round, and smooth, towards the front, where any roughness or projection might have wounded the adjacent viscera, they run out behind and on each side, into long processes, to which processes the muscles necessary to the motions of the trunk are fixed; and fixed with such art, that, whilst the vertebræ supply a basis for the muscles, the muscles help to keep these bones in their position, or by their tendons to tie them together.

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 over-lapping, 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 farther 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 to the bodies of two contiguous vertebra, 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 same purpose of stability; viz. the cheeks of the bars, which pass between the arches, ride 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 slip out of its place. Thus perfectly, by one means or the other, is the danger of slipping laterally, or of being drawn aside out of the line of the back, provided against: and to withstand the bones being pulled as under longitudinally, or in the direction of that 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.

That most important, however, and general property, viz. the strength of the compages, and the security against luxation, was to be still more especially consulted: for where so many joints were concerned, and where, in every one a derangement would have been fatal, it became a subject of studious precaution. For this purpose, the vertebræ 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 slipping, 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 economy may spare himself the disgust of being present at human dissections, and yet learn enough for his information and satisfaction, 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

Upon the whole, and as a guide to those who may be inclined to carry the consideration of this subject farther, there are three views under which the spine ought to be regarded, and in all which it cannot fail to excite our admiration. These views relate to its articulations, its ligaments, and its perforation; and to the corresponding 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 conveniency of the animal. For, whereas, in quadrupeds the number of vertebræ 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 say, in men and quadrupeds, firmness is more consulted; in serpents, pliancy. Yet even pliancy is not obtained at the expense of safety. The back-bone of a serpent, for coherence and flexibility, is one of the most curious pieces of animal mechanism with which we are acquainted. The chain of a

*Der. Phys. Theol. p. 396.