« السابقةمتابعة »
part is not so constructed as to effectuate its pur- | know perhaps as little as we do of the nervous pose whilst it operates according to these laws; fluid. But, magnetic attraction being assumed (it but it is because these laws themselves are not in signifies nothing from what cause it proceeds) all cases equally understood; or, what amounts to we can trace, or there can be winted out to us, nearly the same thing, are not equally exemplified with perfect clearness and certainty, the mechain more simple processes, and more simple ma- nism, viz. the steel bars, the wheels, the joints, chines; that we lay down the distinction, here the wires, by which the motion so much admired proposed, between the mechanical parts and other is communicated to the fingers of the image: and paris of animals and vegetables.
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 iinportance 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, Ist, 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 But whilst I contend for these propositions, I number and variety of the muscles, and the cor- do not exclude myself from asserting, that there responding number and variety of useful powers may be, and that there are other cases, in which, which they supply to the animal; which is asto- although we cannot exhibit mechanism, or prove nishingly great : 3dly, To the judicious (if we indeed that mechanism is employed, we want not may be permitted to use that term, in speaking of sufficient evidence to conduct us to the same conthe Author, or of the works, of nature,) to the clusion. wise and well-contrived disposition of each muscle There is what may be called the chymical part for its specific purpose : for moving the joint this of our frame ; of which, by reason of the imperfecway, and that way, and the other way; for pulling tion of our chymistry, we can attain to no distinct and drawing the part to which it is attached, in å knowledge; I mean, not to a knowledge, either determinate and particular direction; which is a in degree or kind, similar to that which we posmechanical operation, exemplified in a multitude sess of the mechanical part of our frame. It does of instances. To mention only one: The tendon not, therefore, afford the same species of argument of the trochlear muscle of the eye, to the end that as that which mechanism affords; and yet it may it may draw in the line required, is passed through afford an argument in a high degree satisfactory. a cartilaginous ring, at which it is reverted, exact. The gastric juice, or the liquor which digests the ly in the same manner as a rope in a ship is food in the stomachs of animals, is of this class. carried over a block or round a stay, in order to Of all menstrua, it is the most active, the most make it pull in the direction which is wanted. universal. In the human stomach, for instance, All this, as we have said, is mechanical; and is consider what a variety of strange substances, and as accessible to inspection, as capable of being how widely different from one another, it, in a ascertained, as the mechanism of the automaton few hours, reduces to a uniform pulp, milk, or in the Strand. Suppose the automaton to be put mucilage. It seizes upon every thing, it dissolves in motion by a magnet (which is probable,) it the texture of almost every thing that comes in its will supply us with a comparison very apt for our way. The flesh of perhaps all animals; the seeds present purpose. Of the magnetic emluvium, we and fruits of the greatest number of plants; the
monts, and stalks, and leaves, of many, hard and , lation, by which one and the same blood is contough as they are, yield to its powerful pervasion. verted into bone, muscular flesh, nerves, memThe change wrought by it is different from any branes, tendons; things as different as the wood chymnical solution which we can produce, or with and iron, canvass and cordage, of which a ship which we are acquainted, in this respect as well with its furniture is composed. We have no opeas many others, that, in our chymistry, particular ration of art wherewith exactly to compare all this, menstrua act only upon particular substances. Con- for no other reason perhaps than that all operasider moreover, that this tluid, stronger in its ope- tions of art are exceeded by it. No chymical elecration than a caustic alkali or mineral acid, than tion, no chymical analysis or resolution of a subred precipitate, or aqua-fortis itself, is nevertheless stance into its constituent parts, no mechanical as mild, and bland, and inoffensive to the touch or sifting or division, that we are acquainted with, in taste, as saliva or gum-water, which it much re- perfection or variety, come up to animal secretion. sembles. Consider, I say, these several properties Nevertheless, the apparatus and process are obof the digestive organ, and of the juice with which scure; not to say absolutely concealed from our it is supplied, or rather with which it is made to inquiries. In a few, and only a few instances, supply itself, and you will confess it to be entitled we can discern a little of the constitution of a to a name, which it has sometimes received, that gland. In the kidneys of large animals, we can of "the chymical wonder of animal nature." trace the emulgent artery dividing itself into an
Still we are ignorant of the composition of this infinite number of branches; their extremities fluid, and of the mode of its action; by which is every where communicating with little round meant, that we are not capable, as we are in the bodies, in the substance of which bodies the secret mechanical part of our frame, of collating it with of the machinery seems to reside, for there the the operations of art. And this I call the imper- change is made. We can discern pipes laid from fection of our chymistry; for, should the time ever these round bodies toward the pelvis, which is a arrive, which is not perhaps to be despaired of, basin within the solid of the kidney. We can when we can compound ingredients, so as to form discern these pipes joining and collecting together a solvent which will act in the manner in which into larger pipes; and, when so collected, ending the gastric juice acts, we may be able to ascertain in innumerable papillæ, through which the sethe chymical principles upon which its efficacy creted fluid is continually oozing into its receptacle. depends, as well as from what part, and by what This is all we know of the mechanism of a gland, concoction, in the human body, these principles even in the case in which it seems most capable of are generated and derived.
being investigated. Yet to pronounce that we In the mean time, ought that, which is in truth know nothing of animal secretion, or nothing the defect of our chymistry, to hinder us from ac- satisfactorily, and with that concise remark to quiescing in the inference, which a production of dismiss the article from our argument, would be nature, by its place, its properties, its action, its to dispose of the subject very hastily and very irsurprising efficacy, its invaluable use, authorises rationally. For the purpose which we want, that us io draw in respect of a creative design ? 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 Auids 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 fætid 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 com the 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 Akın to secretion, if not the same thing, is assimi- grain in meal fit for the making of bread, the wool
in rovings ready for spinning into threads, the | as, amongst those which have come to our know. sheaf 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
Of the Bones. or successive, upon the material presented to them? I.-I challenge any man to produce, in the He may long to do this to gratify his curiosity; he joints and pivots of the most complicated or the may desire to do it to improve his theoretic know- most flexible machine that was ever contrived, a ledge; or he may have a more substantial reason construction more artificial, or more evidently for requesting it, if he happen, instead of a com- artificial than that which is seen in the vertemon visitor, to be a millwright by profession, or a bræ of the human neck.-Two things were to person sometimes called in to repair such-like be done. The head was to have the power of machines when out of order ; but, for the purpose bending forward and backward, as in the act of ascertaining the existence of counsel and design of nodding, stooping, looking upward or downin the formation of the machine, he wants no such ward; and, at the same time, of turning itself intromission or privity. What he sees, is suffi- round upon the body to a certain extent, the cient. The effect upon the material, the change quadrant we will say, or rather, perhaps, a hunproduced in it, the utility of that change for future dred and twenty degrees of a circle. For these applications, abundantly testify, be the concealed two purposes, two distinct contrivances are empart of the machine or of its construction what it ployed: First, the head rests immediately upon will, the hand and agency of a contriver. 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 a pivot or axle, upon which that upper bone, tothin brine which washes the ball? Why is the gether with the head which it supports, turns synovia of the joints mucilaginous; the bile bitter, freely in a circle; and as far in the circle as the stimulating, and soapy ? Why does the juice, attached muscles permit the head to turn. Thus which flows into the stomach, contain powers, are both motions perfect, without interfering with which make that bowel the great laboratory, as it each other. When we nod the head, we use the is by its situation the recipient, of the materials of hinge-joint, which lies between the head and the future nutrition? These are all fair questions; first bone of the neck. When we turn the head and no answer can be given to them but what calls round, we use the tenon and mortice, which runs in intelligence and intention.
between the first bone of the neck and the second My object in the present chapter has been to We see the same contrivance and the same printeach three things: first, that it is a mistake to ciple employed in the frame or mounting of a telessuppose that, in reasoning from the appearances of cope. Ii is occasionally requisite, that the objectnature, the imperfection of our knowledge propor- end of the instrument be moved up and down, as tionably affects the certainty of our conclusion; well as horizontally or equatorially. For the verfor in many cases it does not affect it at all: se- tical motion, there is a hinge, upon which the condly, that the different parts of the animal frame telescope plays; for the horizontal or equatorial may be classed and distributed, according to the motion, an axis upon which the telescope and the degree of exactness with which we can compare hinge turn round together. And this is exactly them with works of art : thirdly, that the mechani. the mechanism which is applied to the motion of cal parts of our frame, or those in which this com- the head: nor will any one here doubt of the ex. parison is most complete, although constituting, istence of counsel and design, except it be by that probably, the coarsest portions of nature's work- debility of mind, which can trust to its own reamanship, are the most proper to be alleged as sonings in nothing. proofs and specimens of design.
We may add, that it was on another account also, expedient, that the motion of the head back
ward and forward should be performed upon the CHAPTER VIII.
upper surface of the first vertebræ: for if the first Of Mechanical Arrangement in the Human
vertebræ itself had bent forward, it would have Frame.
brought the spinal marrow, at the very beginning
of its course, upon the point of the tooth. We proceed, therefore, to propose certain exam II. Another mechanical contrivance, not unlike des taken out of this class : making choice of such I 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 tho 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 upwani. 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 j 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 hoļlow near each end ing the task, before he be told how the same thing of one bone, to which is fitted a corresponding is eflected 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 tirmness, 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 inanagement 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
III. The spine, or back-bone, is a chain of or twists; or the joints gaping externally, whenjoints of very wonderful construction. Various, ever the body is bent forward,
and the spine theredifficult, and almost inconsistent offices were to be upon made to take the form of a bow. These executed by the same instrument. It was to be dangers, which are mechanical, are mechanically firm, yet flexible: (now I know no chain made by provided against. The vertebræ, by means of art, which is both these ; for by firmness I mean, their processes and projections, and of the articunot only strength, but stability :) firm, to support lations which some of these form with one another the erect position of the body,
flexible, to allow of at their extremities, are so locked in and confined, the bending of the trunk in all degrees of curva- as to maintain, in what are called the bodies or
It was farther also (which is another, and broad surfaces of the bones, the relative position quite a distinct purpose from the rest) to become nearly unaltered; and to throw the change and a pipe or conduit for the safe conveyance from the the pressure, produced by flexion, almost entirely brain, of the most important fluid of the animal upon the intervening cartilages, the springiness frame, that, namely, upon which all voluntary and yielding nature of whose substance admits of motion depends, the spinal marrow; a substance all the motion which is necessary to be performed not only of the first necessity to action, if not to upon them, without any chasms being produced life, but of a nature so delicate and tender, so sus- by a separation of the parts. I say, of all the moceptible, and so impatient of injury, as that any tion which is necessary; for although we bend unusual pressure upon it, or any considerable ob- our backs to every degree almost of inclination, struction of its course, is followed by paralysis or the motion of each vertebra is very small: such is
the advantage we receive from the chain being each side of it, that no pressure which he can use, composed of so many links, the spine of so many will force it out of its place between them. It will bones. Had it consisted of three or four bones give way neither forward nor backward, nor on only; in bending the body, the spinal marrow either side. In whichever direction he pushes, he must have been bruised at every angle. The perceives, in the form, or junction, or over-lapping, reader need not be told, that these intervening car of the bones, an impediment opposed to his attilages are gristles; and he may see them in per- tempt; a check and guard against dislocation. In fection in a loin of veal. Their form also favours one part of the spine, he will find a still farther the same intention. They are thicker before than fortifying expedient, in the mode according to behind; so that, when we stoop forward, the which the ribs are annexed to the spine. Each compressible substance of the cartilage, yielding rib rests upon two vertebra. That is the thing in its thicker and interior part to the force which to be remarked, and any one may remark it in squeezes it, brings the surfaces of the adjoining carving a neck of mutton. The manner of it is vertebræ nearer to the being parallel with one this: the end of the rib is divided by a middle another than they were before, instead of increas- ridge into two surfaces; which surfaces are joined ing the inclination of their planes, which must to the bodies of two contiguous vertebræ, the ridge have occasioned a fissure or opening between them. applying itself to the intervening cartilage. Now Thirdly, for the medullary canal giving out in its this is the very contrivance which is employed course, and in a convenient order a supply of in the famous iron bridge at my door at Bishop nerves to different parts of the body, notches are Wearmouth; and for the same purpose of stability; made in the upper and lower edge of every verte- riz. the cheeks of the bars, which pass between bra; two on each edge; equi-distant on each side the arches, ride across the joints, by which the from the middle line of the back. When the pieces composing each arch are united. Each vertebræ are put together, these notches, exactly cross-bar rests upon two of these pieces at their fitting, form small holes, through which the place of junction; and by that position resists, at nerves, at each articulation, issue out in pairs, in least in one direction, any tendency in either piece to order to send their branches to every part of the slip out of its place. Thus perfecily, by one means body, and with an equal bounty to both sides of or the other, is the danger of slipping laterally, the body. The fourth purpose assigned to the or of being drawn aside out of the line of the back, same instrument, is the insertion of the bases of provided against: and to withstand the bones being the muscles, and the support of the ends of the pulled as under longitudinally, or in the direction ribs; and for this fourth purpose, especially the of that line, a strong membrane runs from one former part of it, a figure, specifically suited to the end of the chain to the other, sufficient to resist design, and unnecessary for the other purposes, is any force which is ever likely to act in the direcgiven to the constituent bones. Whilst they are tion of the back, or parallel to it, and consequently plain, and round, and smooth, towards the front, to secure the whole combination in their places. where any roughness or projection might have The general result is, that not only the motions wounded the adjacent viscera, they run out behind of the human boly necessary for the ordinary of and on each síde, into long processes, to which fices of life are performed with safety, but that it processes the muscles necessary to the motions of is an accident hardly ever heard of, that even the the trunk are fixed; and fixed with such art, that, gesticulations of a harlequin distort his spine. whilst the vertebræ supply a basis for the muscles, Upon the whole, and as a guide to those who the muscles help to keep these bones in their posi- may be inclined to carry the consideration of this tion, or by their tendons to tie them together. subject farther, there are three views under which
That most important, however, and general the spine ought to be regarded, and in all which property, viz. the strength of the compages, and it cannot fail to excite our admiration. These the security against luxation, was to be still more views relate to its articulations, its ligaments, and especially consulted: for where so many joints its perforation; and to the corresponding advanwere concerned, and where, in every one a de- tages which the body derives from it, for action, rangement would have been fatal, it became a for strength, and for that which is essential to subject of studious precaution. For this purpose, every part, a secure communication with the brain. the vertebræ are articulated, that is, the moveable The structure of the spine is not in general joints between them are formed by means of those different in different animals. In the serpent projections of their substance, which we have tribe, however, it is considerably varied; but with mentioned under the name of processes; and a strict reference to the conveniency of the animal. these so lock in with, and overwrap one another For, whereas, in quadrupeds the number of verteas to secure the body of the vertebra not only bræ is from thirty to forty, in the serpent it is from accidentally slipping, but even from being nearly one hundred and fifty: whereas in men pushed out of its place by any violence short of and quadrupeds the surfaces of the bones are fat, that which would break the bone. I have often and these flat surfaces laid one against the other, remarked and admired this structure in the chine and bound tight by sinews; in the serpent, the of a hare. In this, as in many instances, a plain bones play one within another like a ball and observer of the animal economy may spare himself socket,* so that they have a free motion upon one the disgust of being present at human dissections, another in every direction: that is to say, in men and yet learn enough for his information and sa- and quadrupeds, tirmness is more consulted; in tisfaction, by even examining the bones of the serpents, pliancy. Yet even pliancy is not obanimals which come upon his table. Let him tained at the expense of safety. The back-bone take, for example, into his hands, a piece of the of a serpent, for coherence and flexibility, is one clean-picked bone of a hare's back; consisting, we of the most curious pieces of animal mechanism will suppose, of three vertebræ. He will find the with which we are acquainted. The chain of a middle bone of the three so implicated, by means of its projections or processes, with the bone on
* Der. Phys. Theol. p. 396.