in rovings ready for spinning into threads, the sheaf in corn dressed for the mill. Is it necessary that this man, in order to be convinced that design, that intention, that contrivance, has been employed about the machine, should be allowed to pull it to pieces; should be enabled to examine 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.

as, amongst those which have come to our knowledge, appear to be the most striking, and the best understood; but obliged, perhaps, to postpone both these recommendations to a third; that of the example being capable of explanation without plates, or figures, or technical language.

Of the Bones.

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 vertebræ 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.

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. My object in the present chapter has been to We see the same contrivance and the same prin teach three things: first, that it is a mistake to ciple employed in the frame or mounting of a teles suppose that, in reasoning from the appearances of cope. It 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; for in many cases it does not affect 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 examples taken out of this class: making choice of such

well as horizontally or equatorially. For the ver tical 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

death. 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 afterward 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

its means, is seen in what anatomists call the forearm; that is, in the arm between the elbow and the wrist. Here, for the perfect use of the limb, two motions are wanted: a motion at the elbow backward and forward, which is called a reciprocal motion; and a rotatory motion, by which the palm of the hand, as occasion requires, may be tarned upward. How is this managed? the forearm, it is well known, consists of two bones, lying along-side 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 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, 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 vertebræ is very small: 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

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 vertebra. 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 vertebræ, 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 checks 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 of fices 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.

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, notchies 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.

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 fiat, 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 ob tained 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.

watch (I mean the chain which passes between | no account can be given from the structure or the spring-barrel and the fusee,) which aims at exercise of the part. the same properties, is but a bungling piece of workmanship in comparison with that of which we speak.

membrane ties, confines, and holds, the ends of
the bones together; keeping the corresponding
parts of the joint, i. e. the relative convexities and
concavities, in close application to each other.
For the ball and socket-joint, beside the mem-
brane already described, there is in some import-
ant joints, as an additional security, a short,
strong, yet flexible ligament, inserted by one end
into the head of the ball, by the other into the bot-
tom of the cup; which ligament keeps the two parts
of the joint so firmly in their place, that none of
the motions which the limb naturally performs,
none of the jerks and twists to which it is ordi-
narily liable, nothing less indeed than the utmost
and the most unnatural violence, can pull them
asunder. It is hardly imaginable, how great a
force is necessary, even to stretch, still more to
break, this ligament; yet so flexible is it, as to op-
pose no impediment to the suppleness of the joint.
By its situation also, it is inaccessible to injury
from sharp edges. As it cannot be ruptured, (such
is its strength,) so it cannot be cut, except by an
accident which would sever the limb. If I had
been permitted to frame a proof of contrivance,
such as might satisfy the most distrustful inqui-
rer, I know not whether I could have chosen an
example of mechanism more unequivocal, or more
free from objection, than this ligament. Nothing
can be more mechanical; nothing, however sub-
servient to the safety, less capable of being gene-
rated by the action of the joint. I would particu-
larly solicit the reader's attention to this provision,
as it is found in the head of the thigh-bone; to
its strength, its structure, and its use. It is an
instance upon which I lay my hand. One single
fact, weighed by a mind in earnest, leaves often-
times 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 ex-
amples; but for the purpose of strict argument,
one clear instance is sufficient; and not only suf-
ficient, but capable perhaps of generating a firmer
assurance than what can arise from a divided at-
tention.

the binding up of a fracture, where the fillet is al most 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 liable 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 same,-but to barricade the joint on both sides by a continuation of part of the thickest of the bone over it? The 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 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 The suppleness and pliability of the joints, we stronger on the sides than either before or behind, every moment experience; and the firmness of in order that the convexities may play true in animal articulation, the property we have hitherto their concavities, and not be subject to slip side- been considering, may be judged of from this sinways, which is the chief danger; for the muscu-gle observation, that, at any given moment of lar 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," that the knee cannot be completely dislocated without breaking the cross ligaments."* We can hardly help comparing this with

*Ches. Anat. ed. 7th. p. 45.

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