Chapter XI.
Of the Animal Structure Regarded as a Mass

Contemplating an animal body in its collective capacity, we cannot forget to notice what a number of instruments are brought together, and often within how small a compass. It is a cluster of contrivances. In a canary-bird, for instance, and in the single ounce of matter which composes his body—but which seems to be all employed—we have instruments for eating, for digesting, for nourishment, for breathing, for generation, for running, for flying, for seeing, for hearing, for smelling: each appropriate—each entirely different from all the rest.

The human or indeed the animal frame, considered as a mass or assemblage, exhibits in its composition three properties, which have long struck my mind as indubitable evidences not only of design, but of a great deal of attention and accuracy in prosecuting the design.

I. The first is, the exact correspondency of the two sides of the same animal: the right hand answering to the left, leg to leg, eye to eye, one side of the countenance to the other; and with a precision, to imitate which in any tolerable degree, forms one of the difficulties of statuary, and requires, on the part of the artist, a constant attention to this property of his work distinct from every other.

It is the most difficult thing that can be to get a wig made even; yet how seldom is the face awry. And what care is taken that it should not be so, the anatomy of its bones demonstrates. The upper part of the face is composed of thirteen bones, six on each side, answering each to each, and the thirteenth, without a fellow, in the middle. The lower part of the face is in like manner composed of six bones, three on each side, respectively corresponding, and the lower jaw in the centre. In building an arch, could more be done in order to make the curve true, that is, the parts equidistant from the middle, alike in figure and position?

The exact resemblance of the eyes, considering how compounded this organ is in its structure, how various and how delicate are the shades of color with which its iris is tinged; how differently, as to effect upon appearance, the eye may be mounted in its socket, and how differently in different heads eyes actually are set—is a property of animal bodies much to be admired. Of ten thousand eyes, I do not know that it would be possible to match one, except with its own fellow; or to distribute them into suitable pairs by any other selection than that which obtains.

This regularity of the animal structure is rendered more remarkable by the three following considerations:

1. The limbs, separately taken, have not this correlation of parts, but the contrary of it. A knife drawn down the chine cuts the human body into two parts, externally equal and alike; you cannot draw a straight line which will divide a hand, a foot, the leg, the thigh, the cheek, the eye, the ear, into two parts equal and alike. Those parts which are placed upon the middle or partition line of the body, or which traverse that line—as the nose, the tongue, and the lip—may be so divided, or more properly speaking, are double organs; but other parts cannot. This shows that the correspondency which we have been describing does not arise by any necessity in the nature of the subject; for, if necessary, it would be universal; whereas it is observed only in the system or assemblage. It is not true of the separate parts: that is to say, it is found where it conduces to beauty or utility; it is not found where it would subsist at the expense of both. The two wings of a bird always correspond; the two sides of a feather frequently do not. In centipedes, millipedes, and the whole tribe of insects, no two legs on the same side are alike; yet there is the most exact parity between the legs opposite to one another.

2. The next circumstance to be remarked is, that while the cavities of the body are so configurated as externally to exhibit the most exact correspondency of the opposite sides, the contents of these cavities have no such correspondency. A line drawn down the middle of the breast divides the thorax into two sides exactly similar; yet these two sides enclose very different contents. The heart lies on the left side, a lobe of the lungs on the right; balancing each other neither in size nor shape. The same thing holds of the abdomen. The liver lies on the right side, without any similar viscus opposed to it on the left. The spleen indeed is situated over against the liver; but agreeing with the liver neither in bulk nor form. There is no equipollency between these. The stomach is a vessel both irregular in its shape and oblique in its position. The foldings and doublings of the intestines do not present a parity of sides. Yet that symmetry which depends upon the correlation of the sides is externally preserved throughout the whole trunk, and is the more remarkable in the lower parts of it, as the integuments are soft, and the shape, consequently, is not, as the thorax is, by its ribs, reduced by natural stays. It is evident, therefore, that the external proportion does not arise from any equality in the shape or pressure of the internal contents. What is it, indeed, but a correction of inequalities; an adjustment, by mutual compensation, of anomalous forms into a regular congeries; the effect, in a word, of artful, and if we might be permitted so to speak, of studied collocation?

3. Similar also to this is the third observation: that an internal inequality in the feeding vessel is so managed as to produce no inequality of parts, which were intended to correspond. The right arm answers accurately to the left, both in size and shape; but the arterial branches which supply the two arms do not go off from their trunk in a pair, in the same manner, at the same place, or at the same angle. Under which want of similitude, it is very difficult to conceive how the same quantity of blood should be pushed through each artery; yet the result is right: the two limbs which are nourished by them perceive no difference of supply—no effects of excess or deficiency.

Concerning the difference of manner in which the subclavian and carotid arteries, upon the different sides of the body, separate themselves from the aorta, Cheselden seems to have thought, that the advantage which the left gain by going off at an angle much more acute than the right, is made up to the right by their going off together in one branch.* It is very possible that this may be the compensating contrivance; and if it be so, how curious—how hydrostatical!

II. Another perfection of the animal mass is the package. I know nothing which is so surprising. Examine the contents of the trunk of any large animal. Take notice how soft, how tender, how intricate they are; how constantly in action, how necessary to life! Reflect upon the danger of any injury to their substance, any derangement to their position, any obstruction to their office. Observe the heart pumping at the centre, at the rate of eighty strokes in a minute; one set of pipes carrying the stream away from it, another set bringing in its course, the fluid back to it again; the lungs performing their elaborate office, namely, distending and contracting their many thousand vesicles by a reciprocation which cannot cease for a minute; the stomach exercising its powerful chemistry; the bowels silently propelling the changed aliment—collecting from it, as it proceeds, and transmitting to the blood an incessant supply of prepared and assimilated nourishment; that blood pursuing its course; the liver, the kidneys, the pancreas, the parotid, with many other known and distinguishable glands, drawing off from it, all the while, their proper secretions. These several operations, together with others more subtile but less capable of being investigated, are going on within us at one and the same time. Think of this; and then observe how the body itself, the case which holds this machinery, is rolled, and jolted, and tossed about, the mechanism remaining unhurt, and with very little molestation even of its nicest motions. Observe a rope-dancer, a tumbler, or a monkey—the sudden inversions and contortions which the internal parts sustain by the postures into which their bodies are thrown; or rather observe the shocks which these parts, even in ordinary subjects, sometimes receive from falls and bruises, or by abrupt jerks and twists, without sensible or with soon recovered damage. Observe this, and then reflect how firmly every part must be secured, how carefully surrounded, how well tied down and packed together.

This property of animal bodies has never, I think, been considered under a distinct head, or so fully as it deserves. I may be allowed therefore, in order to verify my observation concerning it, to set forth a short anatomical detail, though it oblige me to use more technical language than I should wish to introduce into a work of this kind.

1. The heart—such care is taken of the centre of life—is placed between two soft lobes of the lungs; is tied to the mediastinum and to the pericardium; which pericardium is not only itself an exceedingly strong membrane, but adheres firmly to the duplicature of the mediastinum, and by its point, to the middle tendon of the diaphragm. The heart is also sustained in its place by the great bloodvessels which issue from it.*

2. The lungs are tied to the sternum by the mediastinum before; to the vertebrae, by the pleura behind. It seems indeed to be the very use of the mediastinum—which is a membrane that goes straight through the middle of the thorax, from the breast to the back—to keep the contents of the thorax in their places; in particular to hinder one lobe of the lungs from incommoding another, or the parts of the lungs from pressing upon each other when we lie on one side.†

3. The liver is fastened in the body by two ligaments: the first, which is large and strong, comes from the covering of the diaphragm, and penetrates the substance of the liver; the second is the umbilical vein, which, after birth, degenerates into a ligament. The first, which is the principal, fixes the liver in its situation while the body holds an erect posture; the second prevents it from pressing upon the diaphragm when we lie down; and both together sling or suspend the liver when we lie upon our backs, so that it may not compress or obstruct the ascending vena cava,* to which belongs the important office of returning the blood from the body to the heart.

4. The bladder is tied to the navel by the urachus, transformed into a ligament: thus, what was a passage for urine to the foetus, becomes, after birth, a support or stay to the bladder. The peritoneum also keeps the viscera from confounding themselves with, or pressing irregularly up the bladder; for the kidneys and bladder are contained in a distinct duplicature of that membrane, being thereby partitioned off from the other contents of the abdomen.

5. The kidneys are lodged in a bed of fat.

6. The pancreas, or sweetbread, is strongly tied to the peritoneum, which is the great wrapping-sheet that encloses all the bowels contained in the lower belly.†

7. The spleen also is confined to its place by an adhesion to the peritoneum and diaphragm, and by a connection with the omentum.‡ It is possible, in my opinion, that the spleen may be merely a stuffing, a soft cushion to fill up a vacancy or hollow, which, unless occupied, would leave the package loose and unsteady; for, supposing that it answers no other purpose than this, it must be vascular, and admit of a circulation through it, in order to be kept alive, or be a part a living body.

8. The omentum, epiploon, or caul, is an apron tucked up, or doubling upon itself, at its lowest part. The upper edge is tied to the bottom of the stomach, to the spleen, as has already been observed, and to part of the duodenum. The reflected edge also, after forming the doubling, comes up behind the front flap, and is tied to the colon and adjoining viscera.*

9. The septa of the brain probably prevent one part of the organ from pressing with too great a weight upon another part. The processes of the dura mater divide the cavity of the skull, like so many inner partition walls, and thereby confine each hemisphere and lobe of the brain to the chamber which is assigned to it, without its being liable to rest upon or intermix with the neighboring parts. The great art and caution of packing is to prevent one thing hurting another. This, in the head, the chest, and the abdomen of an animal body is, among other methods, provided for by membranous partitions and wrappings, which keep the parts separate.

The above may serve as a short account of the manner in which the principal viscera are sustained in their places. But of the provisions for this purpose, by far, in my opinion, the most curious, and where also such a provision was most wanted, is in the guts. It is pretty evident that a long narrow tube—in man, about five times the length of the body—laid from side to side in folds upon one another, winding in oblique and circuitous directions, composed also of a soft and yielding substance, must, without some extraordinary precaution for its safety, be continually displaced by the various, sudden, and abrupt motions of the body which contains it. I should expect that, if not bruised or wounded by every fall, or leap, or twist, it would be entangled, or be involved with itself; or, at the least, slipped and shaken out of the order in which it is disposed, and which order is necessary to be preserved for the carrying on of the important functions which it has to execute in the animal economy. Let us see, therefore, how a danger so serious, and yet so natural to the length, narrowness, and tubular form of the part, is provided against. The expedient is admirable, and it is this. The intestinal canal, throughout its whole process, is knit to the edge of a broad fat membrane called the mesentery. It forms the margin of this mesentery, stitched and fastened to it like the edging of a ruffle; being four times as long as the mesentery itself, it is what a seamstress would call "puckered or gathered on" to it. This is the nature of the connection of the gut with the mesentery; and being thus joined to, or rather made a part of the mesentery, it is folded and wrapped up together with it. Now the mesentery having a considerable dimension in breadth, being in its substance withal both thick and suety, is capable of a close and safe folding, in comparison of what the intestinal tube would admit of, if it had remained loose. The mesentery likewise not only keeps the intestinal canal in its proper place and position under all the turns and windings of its course, but sustains the numberless small vessels, the arteries, the veins, the lympheducts, and above all, the lacteals, which lead from or to almost every point of its coats and cavity. This membrane, which appears to be the great support and security of the alimentary apparatus, is itself strongly tied to the first three vertebra of the loins.*

III. A third general property of animal forms is beauty. I do not mean relative beauty, or that of one individual above another of the same species, or of one species compared with another species; but I mean, generally, the provision which is made in the body of almost every animal to adapt its appearance to the perception of the animals with which it converses. In our own species, for example, only consider what the parts and materials are of which the fairest body is composed; and no farther observation will be necessary to show how well these things are wrapped up, as to form a mass which shall be capable of symmetry in its proportion, and of beauty in its aspect; how the bones are covered, the bowels concealed, the roughnesses of the muscle smoothed and softened; and how over the whole is drawn an integument which converts the disgusting materials of a dissecting-room into an object of attraction to the sight, or one upon which it rests at least with ease and satisfaction. Much of this effect is to be attributed to the intervention of the cellular or adipose membrane, which lies immediately under the skin; is a kind of lining to it; is moist, soft, slippery, and compressible; everywhere filling up the interstices of the muscles, and forming thereby their roundness and flowing line, as well as the evenness and polish of the whole surface.

All which seems to be a strong indication of design, and of a design studiously directed to this purpose. And it being once allowed that such a purpose existed with respect to any of the productions of nature, we may refer, with a considerable degree of probability, other particulars to the same intention; such as the tints of flowers, the plumage of birds, the furs of beasts, the bright scales of fishes, the painted wings of butterflies and beetles, the rich colors and spotted lustre of many tribes of insects.

There are parts also of animals ornamental, and the properties by which they are so, not subservient, that we know of, to any other purpose. The irides of most animals are very beautiful, without conducing at all, by their beauty, to the perfection of vision; and nature could in no part have employed her pencil to so much advantage, because no part presents itself so conspicuously to the observer, or communities so great an effect to the whole aspect.

In plants, especially in the flowers of plants, the principle of beauty holds a still more considerable place in their composition—is still more confessed than in animals. Why, for one instance out of a thousand, does the corolla of the tulip, when advanced to its size and maturity, change its color? The purposes, so far as we can see, of vegetable nutrition might have been carried on as well by its continuing green. Or, if this could not be, consistently with the progress of vegetable life, why break into such a variety of colors? This is no proper effect of age, or of declension in the ascent of the sap; for that, like the autumnal tints, would have produced one color on one leaf, with marks of fading and withering. It seems a lame account to call it, as it has been called, a disease of the plant. Is it not more probable that this property, which is independent, as it should seem, of the wants and utilities of the plant, was calculated for beauty, intended for display?

A ground, I know, of objection has been taken against the whole topic of argument, namely, that there is no such thing as beauty at all: in other words, that whatever is useful and familiar, comes of course to be thought beautiful; and that things appear to be so, only by their alliance with these qualities. Our idea of beauty is capable of being in so great a degree modified by habit, by fashion, by the experience of advantage or pleasure, and by associations arising out of that experience, that a question has been made whether it be not altogether generated by these causes, or would have any proper existence without them. It seems, however, a carrying of the conclusion too far, to deny the existence of the principle, namely, native capacity of perceiving beauty, on account of an influence, or of varieties proceeding from that influence, to which it is subject, seeing that principles the most acknowledged are liable to be affected in the same manner. I should rather argue thus: the question respects objects of sight. Now every other sense has its distinction of agreeable and disagreeable. Some tastes offend the palate, others gratify it. In brutes and insects, this distinction is stronger and more regular than in man. Every horse, ox, sheep, swine, when at liberty to choose, and when in a natural state, that is, when not vitiated by habits forced upon it, eats and rejects the same plants. Many insects which feed upon particular plants, will rather die than change their appropriate leaf. All this looks like a determination in the sense itself to particular tastes. In like manner, smells affect the nose with sensations pleasurable or disgusting. Some sounds, or compositions of sound, delight the ear; others torture it. Habit can do much in all these cases—and it well for us that it can, for it is this power which reconciles us to many necessities; but has the distinction, in the mean time, of agreeable and disagreeable no foundation in the sense itself? What is true of the other senses is most probably true of the eye—the analogy is irresistible—namely, that there belongs to it an original constitution, fitted to receive pleasure from some impressions, and pain from others.

I do not, however, know that the argument which alleges beauty as a final cause rests upon this concession. We possess a sense of beauty, however we come by it. It in fact exists. Things are not indifferent to this sense; all objects do not suit it: many, which we see, are agreeable to it; many others disagreeable. It is certainly not the effect of habit upon the particular object, because the most agreeable objects are often the most rare; many which are very common, continue to be offensive. If they be made supportable by habit, it is all which habit can do; they never become agreeable. If this sense, therefore, be acquired, it is a result—the produce of numerous and complicated actions of external objects upon the senses, and of the mind upon its sensations. With this result there must be a certain congruity, to enable any particular object to please; and that congruity, we contend, is consulted in the aspect which is given to animal and vegetable bodies.

IV. The skin and covering of animals is that upon which their appearance chiefly depends; and it is that part which, perhaps, in all animals, is most decorated, and most free from impurities. But were beauty or agreeableness of aspect entirely out of the question, there is another purpose answered by this integument, and by the collocation of the parts of the body beneath it, which is of still greater importance; and that purpose is concealment. Were it possible to view through the skin the mechanism of our bodies, the sight would frighten us out of our wits. "Durst we make a single movement," asks a lively French writer, "or stir a step from the place we were in, if we saw our blood circulating, the tendons pulling, the lungs blowing, the humors filtrating, and all the incomprehensible assemblage of fibres, tubes, pumps, valves, currents, pivots, which sustain an existence at once so frail and so presumptuous?"

V. Of animal bodies, considered as masses, there is another property more curious than it is generally thought to be, which is the faculty of standing; and it is more remarkable in two-legged animals than in quadrupeds, and most of all, as being the tallest and resting upon the smallest base, in man. There is more, I think, in the matter than we are aware of. The statue of a man placed loosely upon a pedestal, would not be secure of standing half an hour. You are obliged to fix its feet to the block by bolts and solder, or the first shake, the first gust of wind, is sure to throw it down. Yet this statue shall express all the mechanical proportions of a living model. It is not therefore the mere figure, or merely placing the centre of gravity within the base, that is sufficient. Either the law of gravitation is suspended in favor of living substances, or something more is done for them, in order to enable them to uphold their posture. There is no reason whatever to doubt, but that their parts descend by gravitation in the same manner as those of dead matter. The gift therefore appears to me to consist in a faculty of perpetually shifting the centre of gravity, by a set of obscure, indeed, but of quick-balancing actions, so as to keep the line of direction, which is a line drawn from that centre to the ground, within its prescribed limits.

Of these actions it may be observed, first, that they in part constitute what we call strength. The dead body drops down. The mere adjustment therefore of weight and pressure, which may be the same the moment after death as the moment before, does not support the column. In cases also of extreme weakness, the patient cannot stand upright. Secondly, that these actions are only in a small degree voluntary. A man is seldom conscious of his voluntary powers in keeping himself upon his legs. A child learning to walk is the greatest posture-master in the world; but art, if it may be so called, sinks into habit, and he is soon able to poise himself in a great variety of attitudes, without being sensible either of caution or effort. But still there must be an aptitude of parts, upon which habit can thus attach—a previous capacity of motions which the animal is thus taught to exercise; and the facility with which this exercise is acquired, forms one object of our admiration. What parts are principally employed, or in what manner each contributes to its office, is, as has already been confessed, difficult to explain. Perhaps the obscure motion of the bones of the feet may have their share in this effect. They are put in action by every slip or vacillation of the body, and seem to assist in restoring its balance. Certain it is, that this circumstance in the structure of the foot, namely, its being composed of many small bones, applied to and articulating with one another by diversely shaped surfaces, instead of being made of one piece, like the last of a shoe, is very remarkable.

I suppose also, that it would be difficult to stand firmly upon stilts or wooden legs, though their base exactly imitated the figure and dimensions of the sole of the foot. The alternation of the joints, the knee-joint bending backward, the hip-joint forward; the flexibility, in every direction, of the spine, especially in the loins and neck, appear to be of great moment in preserving the equilibrium of the body. With respect to this last circumstance, it is observable that the vertebrae are so confined by ligaments as to allow no more slipping upon their bases than what is just sufficient to break the shock which any violent motion may occasion to the body. A certain degree also of tension of the sinews appears to be essential to an erect posture; for it is by the loss of this that the dead or paralytic body drops down.

The whole is a wonderful result of combined powers and of very complicated operations. Indeed, that standing is not so simple a business as we imagine it to be, is evident from the strange gesticulations of a drunken man, who has lost the government of the centre of gravity.

We have said that this property is the most worthy of observation in the human body; but a bird resting upon its perch, or hopping upon a spray, affords no mean specimen of the same faculty. A chicken runs off as soon as it is hatched from the egg; yet a chicken, considered geometrically, and with relation to its centre of gravity, its line of direction, and its equilibrium, is a very irregular solid. Is this gift, therefore, or instruction? May it not be said to be with great attention that nature has balanced the body upon its pivots?

I observe also in the same bird a piece of useful mechanism of this kind. In the trussing of a fowl, upon bending the legs and thighs up towards the body, the cook finds that the claws close of their own accord. Now let it be remembered, that this is the position of the limbs in which the bird rests upon its perch. And in this position it sleeps in safety; for the claws do their office in keeping hold of the support, not by any exertion of voluntary power which sleep might suspend, but by the traction of the tendons in consequence of the attitude which the legs and thighs take by the bird sitting down, and to which the mere weight of the body gives the force that is necessary.

VI. Regarding the human body as a mass; regarding the general conformations which obtain in it; regarding also particular parts in respect to those conformations, we shall be led to observe what I call "interrupted analogies." The following are examples of what I mean by these terms; and I do not know how such critical deviations can, by any possible hypothesis, be accounted for without design.

1. All the bones of the body are covered with a periosteum except the teeth, where it ceases; and an enamel of ivory, which saws and files will hardly touch, comes into its place. No one can doubt of the use and propriety of this difference—of the "analogy" being thus "interrupted"—of the rule which belongs to the conformation of the bones stopping where it does stop; for, had so exquisitely sensible a membrane as the periosteum invested the teeth as it invests every other bone of the body, their action, necessary exposure, and irritation, would have subjected the animal to continual pain. General as it is, it was not the sort of integument which suited the teeth: what they stood in need of was a strong, hard, insensible, defensive coat; and exactly such a covering is given to them in the ivory enamel which adheres to their surface.

2. The scarfskin, which clothes all the rest of the body, gives way, at the extremities of the toes and fingers, to nails. A man has only to look at his hand, to observe with what nicety and precision that covering, which extends over every other part, is here superseded by a different substance and a different texture. Now, if either the rule had been necessary, or the deviation from it accidental, this effect would not be seen. When I speak of the rule being necessary, I mean the formation of the skin upon the surface being produced by a set of causes constituted without design, and acting as all ignorant causes must act, by a general operation. Were this the case, no account could be given of the opera­tion being suspended at the fingers' ends, or on the back part of the fingers, and not on the fore part. On the other hand, if the deviation were accidental, an error, an anomalism—were it any thing else than settled by intention—we should meet with nails upon other parts of the body; they would be scattered over the surface, like warts or pimples.

3. All the great cavities of the body are enclosed by membranes, except the skull. Why should not the brain be content with the same covering as that which serves for the other principal organs of the body? The heart, the lungs, the liver, the stomach, the bowels, have all soft integuments, and nothing else. The muscular coats are all soft and membranous. I can see a reason for this distinction in the final cause, but in no other. The importance of the brain to life—which experience proves to be immediate—and the extreme tenderness of its substance, make a solid case more necessary for it than for any other part; and such a case the hardness of the skull supplies. When the smallest portion of this natural casket is lost, how carefully, yet how imperfectly, is it replaced by a plate of metal. If an anatomist should say that this bony protection is not confined to the brain, but is extended along the course of the spine, I answer that he adds strength to the argument.  If he remark that the chest also is fortified by bones, I reply that I should have alleged this instance myself, if the ribs had not appeared subservient to the purpose of motion as well as of defence. What distinguishes the skull from every other cavity is, that the bony covering completely surrounds its contents, and is calculated, not for motion, but solely for defence. Those hollows, likewise, and inequalities which we observe in the inside of the skull, and which exactly fit the folds of the brain, answer the important design of keeping the substance of the brain steady, and of guarding it against concussions.

† Keill's Anat., p. 57

‡ Ches. Anat., p. 167