and is simple. Herein the muscular system may be said to bear a perfect resemblance to our works of art. An artist does not alter the native quality of his materials, or their laws of action. He takes these as he finds them. His skill and ingenuity are employed in turning them, such as they are, to his account, by giving to the parts of his machine a form and relation, in which these unalterable properties may operate to the production of the effects in contracted, the former cannot act with free- IV. The following is oftentimes the case with the muscles. Their action is wanted, where their situation would be inconvenient. In which case, the body of the muscle is placed in some commodious position at a distance, and made to communicate with the point of action by slender strings, or wires. If the muscles which move the fingers, had been placed in the palm or back of the hand, they would have swelled that part to an awkward and clumsy thickness. The beauty, the proportions of the part, would have been destroyed. They are therefore disposed in the arm, and even up to the elbow; and act by long tendons, strapped down at the wrist, and passing under the ligaments to the fingers, and to the joints of the fingers, which they are severally to move. In like manner, the muscles which move the toes, and many of the joints of the foot, how gracefully are they disposed in the calf of the leg, instead of forming an unwieldy tumefaction in the foot itself! The observation may be repeated of the muscle which draws the nictitating membrane over the eye. Its office is in the front of the eye; but its body is lodged in the back part of the globe, where it lies safe, and where it encumbers nothing. 66 VI. The ejaculations can never too often be repeated-How many things must go right for us to be an hour at ease! how many more for us to be vigorous and active! Yet vigour and activity are, in a vast plurality of instances, preserved in human bodies, notwithstanding that they depend upon so great a number of instruments of motion, and notwithstanding that the defect or disorder sometimes of a very small instrument, of a single pair, for instance, out of the four hundred and forty-six muscles which are employed, may be attended with grievous inconveniency. There is piety and good sense in the following observation, taken out of the Religious Philosopher: “With much compassion," says this writer, as well as astonishment at the goodness of our loving Creator, have I considered the sad state of a certain gentleman, who, as to the rest, was in pretty good health, but only wanted the use of these two little muscles that serve to lift up the eyelids, and so had almost lost the use of his sight, being forced, as long as this defect lasted, to shove up his eyelids every moment with his own hands!"-In general we may remark in how small a degree those, who enjoy the perfect use of their organs, know the comprehensiveness of the blessing, the variety of their obligation. They perceive a result, but they think little of the multitude of concurrences and rectitudes which go to form it. V. The great mechanical variety in the fiBeside these observations, which belong to gure of the muscles may be thus stated. It the muscular organ as such, we may notice appears to be a fixed law, that the contraction some advantages of structure which are more of a muscle shall be towards its centre. There- conspicuous in muscles of a certain class or fore the subject for mechanism on each occa-description than in others. Thus : sion is, so to modify the figure, and adjust the I. The variety, quickness, and precision, of position of the muscle, as to produce the motion required, agreeably with this law. This can only be done by giving to different mus. cles a diversity of configuration, suited to their several offices, and to their situation with respect to the work which they have to perform. On which account we find them under a multiplicity of forms and attitudes; sometimes with double, sometimes with treble tendons, sometimes with none; sometimes one tendon to several muscles, at other times one muscle to several tendons. The shape of the organ is susceptible of an incalculable variety, whilst the original property of the muscle, the law and line of its contraction, remains the same, Keil's Anatomy, p. 295. ed. 3. which muscular motion is capable, are seen, I think, in no part so remarkably as in the tongue. It is worth any man's while to watch the agility of his tongue; the wonderful promptitude, with which it executes changes of position, and the perfect exactness. Each syllable of articulated sound requires for its utterance a specific action of the tongue, and of the parts adjacent to it. The disposition and configuration of the mouth, appertaining to every letter and word, is not only peculiar, but, if nicely and accurately attended to, perceptible to the sight; insomuch, that curious persons have availed themselves of this circumstance to teach the deaf to speak, and to understand what is said by others. In the same person, and after his habit of speaking is formed, one, and only one, position of the parts, will produce a given gine this to be done simply by the weight of articulate sound correctly. How instantane- the food itself, it in truth is not so, even in ously are these positions assumed and dismissed; the upright posture of the human neck; and how numerous are the permutations, how va- most evidently is not the case with quadrupeds, rious, yet how infallible! Arbitrary and an- with a horse for instance, in which, when pastic variety is not the thing we admire; but va- turing, the food is thrust upward by muscular riety obeying a rule, conducing to an ef- strength, instead of descending of its own acfect, and commensurate with exigencies infi- cord. nitely diversified. I believe also that the ana- In the mean time, and within the same catomy of the tongue corresponds with these ob-vity, is going on another business, altogether servations upon its activity. The muscles of different from what is here described, that the tongue are so numerous, and so implicat- of respiration and speech. In addition thereed with one another, that they cannot be trac-fore to all that has been mentioned, we have ed by the nicest dissection; nevertheless (which a passage opened, from this cavity to the lungs, is a great perfection of the organ) neither the for the admission of air, exclusively of every number, nor the complexity, nor what might other substance; we have muscles, some in seem to be the entanglement of its fibres, in the larynx, and without number in the tongue, anywise impede its motion, or render the de- for the purpose of modulating that air in its termination or success of its efforts uncertain. passage, with a variety, a compass, and precision, of which no other musical instrument I here entreat the reader's permission to step is capable. And lastly, which in my opinion a little out of my way, to consider the parts of crowns the whole as a piece of machinery, we the mouth, in some of their other properties. have a specific contrivance for dividing the It has been said, and that by an eminent phy-pneumatic part from the mechanical, and for siologist, that whenever nature attempts to preventing one set of actions interfering with work two or more purposes by one instrument, the other. Where various functions are unitshe does both, or all, imperfectly. Is this true ed, the difficulty is to guard against the inconof the tongue, regarded as an instrument of veniencies of a too great complexity. In no speech, and of taste; or regarded as an instru-apparatus put together by art, and for the purment of speech, of taste, and of deglutition? poses of art, do I know such multifarious uses So much otherwise, that many persons, that so aptly combined, as in the natural organiza. is to say, nine hundred and ninety-nine per- tion of the human mouth; or where the struc sons out of a thousand, by the instrumentali-ture, compared with the uses, is so simple. The ty of this one organ, talk, and taste, and swal- mouth, with all these intentions to serve, is a low very well. In fact, the constant warmth single cavity; is one machine; with its parts and moisture of the tongue, the thinness of neither crowded nor confused, and each unem. the skin, the papillæ upon its surface, qualify barrassed by the rest: each at least at liberty this organ for its office of tasting, as much as in a degree sufficient for the end to be attain its inextricable multiplicity of fibres do for ed. If we cannot eat and sing at the same the rapid movements which are necessary to moment, we can eat one moment and sing the speech. Animals which feed upon grass, have next: the respiration proceeding freely all the their tongues covered with a perforated skin, while. so as to admit the dissolved food to the papil- There is one case however of this double læ underneath, which, in the meantime, re-office, and that of the earliest necessity, which main defended from the rough action of the the mouth alone could not perform; and that unbruised spicula. is, carrying on together the two actions of There are brought together within the ca- sucking and breathing. Another ronte therevity of the mouth more distinct uses, and parts fore is opened for the air, namely, through the executing more distinct offices, than I think nose, which lets the breath pass backward and can be found lying so near to one another, or forward, whilst the lips, in the act of sucking, within the same compass, in any other portion are necessarily shut close upon the body from of the body; viz. teeth of different shape, first which the nutriment is drawn. This is a cirfor cutting, secondly for grinding; muscles, cumstance which always appeared to me wormost artificially disposed for carrying on the thy of notice. The nose would have been necompound motion of the lower jaw, half later-cessary, although it had not been the organ of al and half vertical, by which the mill is work-smelling. The making it the seat of a sense, ed: fountains of saliva, springing up in differ- was superadding a new use to a part already ent parts of the cavity for the moistening of wanted; was taking a wise advantage of an the food, whilst the mastication is going on: antecedent and a constitutional necessity. glands to feed the fountains; a muscular constriction of a very peculiar kind in the back But to return to that which is the proper part of the cavity, for the guiding of the pre-subject of the present section, the celerity pared aliment into its passage towards the sto- and precision of muscular motion. These quamach, and in many cases for carrying it a-lities may be particularly observed in the exe long that passage; for, although we may ima- cution of many pieces of instrumental music, : in which the changes produced by the hand of A man in an asthma is the only man who the musician are exceedingly rapid; are ex- knows how to estimate it. actly measured, even when most minute; and IV. Mr. Home has observed, that the most display, on the part of the muscles, an obedi- important and the most delicate actions are ence of action, alike wonderful for its quick-performed in the body by the smallest muscles: ness and its correctness. and he mentions, as his examples, the muscles Or let a person only observe his own hand which have been discovered in the iris of the whilst he is writing; the number of muscles, eye, and the drum of the ear. which are brought to bear upon the pen; how of these muscles is astonishing. They are miThe tenuity the joint and adjusted operation of several ten-croscopic hairs; must be magnified to be visidons is concerned in every stroke, yet that five ble; yet are they real, effective muscles and hundred such strokes are drawn in a minute. not only such, but the grandest and most preNot a letter can be turned without more than cious of our faculties, sight and hearing, deone, or two, or three tendinous contractions,pend upon their health and action. definite, both as to the choice of the tendon, V. The muscles act in the limbs with what and as to the space through which the contrac-is called a mechanical disadvantage. The mus tion moves; yet how currently does the work proceed! and when we look at it, how faithful have the muscles been to their duty, how true to the order which endeavour or habit hath inculcated! For let it be remembered, that, whilst a man's hand-writing is the same, an exactitude of order is preserved, whether he write well or ill. These two instances of music and writing, show not only the quickness and precision of muscular action, but the docility. cle at the shoulder, by which the arm is raised, is fixed nearly in the same manner as the load is fixed upon a steelyard, within a few decimals, we will say, of an inch, from the centre upon which the steelyard turns. In this situation, we find that a very heavy draught is no more than sufficient to countervail the force of a small lead plummet, placed upon the long arm of the steelyard, at the distance of perhaps fifteen or twenty inches from the II. Regarding the particular configuration centre and on the other side of it. And this of muscles, sphincter or circular muscles appear is the disadvantage which is meant. And an to me admirable pieces of mechanism. It is absolute disadvantage, no doubt, it would be, the muscular power most happily applied; the if the object were, to spare the force of mussame quality of the muscular substance, but cular contraction. But observe how condu under a new modification. The circular dis-cive is this constitution to animal conveniency. position of the fibres is strictly mechanical; but, though the most mechanical, is not the only thing in sphincters which deserves our notice. The regulated degree of contractile force with which they are endowed, sufficient for retention, yet vincible when requisite, together with their ordinary state of actual con-ent collocation of the muscles, might be better traction, by means of which their dependence upon the will is not constant, but occasional, gives to them a constitution, of which the conveniency is inestimable. This their semivoluntary character, is exactly such as suits with the wants and functions of the animal. Mechanism has always in view one or other of these two purposes; either to move a great weight slowly, and through a small space, or to move a little weight rapidly, through a considerable sweep. For the former of these purposes, a different species of lever, and a differ than the present; but for the second, the present structure is the true one. Now so it hap pens, that the second, and not the first, is that which the occasions of animal life principally call for. In what concerns the human body, it is of much more consequence to any man to III. We may also, upon the subject of mus-be able to carry his hand to his head with due cles, observe, that many of our most import-expedition, than it would be to have the power ant actions are achieved by the combined help of raising from the ground a heavier load (of of different muscles. Frequently, a diagonal two or three more hundred weight, we will motion is produced, by the contraction of ten- suppose,) than he can lift at present. This dons pulling in the direction of the sides of the last is a faculty, which, on some extraordinary parallelogram. This is the case, as hath been occasions, he may desire to possess: but the already noticed, with some of the oblique nu- other is what he wants and uses every hour or tations of the head. Sometimes the number minute. In like manner, a husbandman or a of co-operating muscles is very great. Dr.gardener will do more execution, by being able Nieuentyt, in the Leipsic Transactions, reck- to carry his scythe, his rake, or his flail, with ons up a hundred muscles that are employed a sufficient dispatch through a sufficient space, every time we breathe; yet we take in, or let than if, with greater strength, his motions out, our breath, without reflecting what a work were proportionably more confined, and slow. is thereby performed; what an apparatus is It is the same with a mechanic in the use of laid in, of instruments for the service, and how his tools. It is the same also with other animany such contribute their assistance to the mals in the use of their limbs. In general. effect. Breathing with ease, is a blessing of the vivacity of their motions would be ill exevery moment; yet, of all others, it is that which we possess with the least consciousness. * Phil. Trans. part i. 1800. p. 8. changed for greater force under a clumsier | nothing, I believe, in a silk or cotton mill, in structure. We have offered our observations upon the structure of muscles in general; we have also noticed certain species of muscles; but there are also single muscles, which bear marks of mechanical contrivance, appropriate as well as particular. Out of many instances of this kind, we select the following: the belts, or straps, or ropes by which motion is communicated from one part of the machine to another, that is more artificial, or more evi dently so than this perforation. to the foot. The effect of the ligament as a bandage, can be made evident to the senses; for if it be cut, the tendons start up. The simplicity, yet the clearness of this contri vance, its exact resemblance to established resources of art, place it amongst the most indubitable manifestations of design with which we are acquainted. III. The next circumstance which I shall mention, under this head of muscular arrange. ment, is so decisive a mark of intention, that it always appeared to me to supersede, in some I. Of muscular actions, even of those which measure, the necessity of seeking for any other are well understood, some of the most curious observation upon the subject: and that cir. are incapable of popular explanation; at least, cumstance is, the tendons, which pass from without the aid of plates and figures. This is the leg to the foot, being bound down by a liThe foot is placed at a in a great measure the case, with a very fami-gament at the ankle. liar, but, at the same time, a very complicat-considerable angle with the leg. It is manied motion,—that of the lower jaw; and with fest, therefore, that flexible strings, passing the muscular structure by which it is produc-along the interior of the angle, if left to themed. One of the muscles concerned may, how-selves, would, when stretched, start from it. ever, be described in such a manner, as to be, The obvious preventive is to tie them down. I think, sufficiently comprehended for our pre- | And this is done in fact. Across the instep, sent purpose. The problem is to pull the low- or rather just above it, the anatomist finds a er jaw down. The obvious method should seem strong ligament. under which the tendons pass to be, to place a strait muscle, viz. to fix a string from the chin to the breast, the contraction of which would open the mouth, and produce the motion required at once. But it is evident that the form and liberty of the neck forbid a muscle being laid in such a position; and that, consistently with the preservation of this form, the motion, which we want, must be effectuated by There is also a farther use to be made of the some muscular mechanism disposed farther back in the jaw. The mechanism adopted is as fol- present example, and that is, as it precisely con lows. A certain muscle called the diagastric, ris-tradicts the opinion, that the parts of animals es on the side of the face, considerably above the may have been all formed by what is called ap insertion of the lower jaw, and comes down, be-petency, i. e. endeavour, perpetuated, and im ing converted in its progress into a round ten-perceptibly working its effect, through an indon. Now it is manifest that the tendon, whilst calculable series of generations. We have here it pursues a direction descending towards the no endeavour, but the reverse of it; a constant jaw, must, by its contraction, pull the jaw up, renitency and reluctance. The endeavour is instead of down. What then was to be done? all the other way. The pressure of the liga. This, we find, is done: The descending ten-ment constrains the tendons; the tendons redon, when it is got low enough, is passed act upon the pressure of the ligament. It is through a loop, or ring, or pulley, in the os impossible that the ligament should ever have hyoïdes, and then made to ascend; and, hav- been generated by the exercise of the tendon, ing thus changed its line of direction, is insert- or in the course of that exercise, forasmuch as ed into the inner part of the chin: by which the force of the tendon perpendicularly resists device, viz. the turn at the loop, the action of the fibre which confines it, and is constantly the muscle (which in all muscles is contrac- endeavouring, not to form, but to rupture and tion) that before would have pulled the jaw displace, the threads of which the ligament is up, now as necessarily draws it down. "The composed. mouth," says Heister, "is opened by means of this trochlea in a most wonderful and elegant manner." imagination. Keill has reckoned up, in the human body, four hundred and forty-six muscles, dissectible II. What contrivance can be more mecha- and describable; and hath assigned a use to nical than the following, viz. a slit in one ten-every one of the number. This cannot be all don to let another tendon pass through it? This structure is found in the tendons which move the toes and fingers. The long tendon, as it is called, in the foot, which bends the first joint of the toe, passes through the short tendon which bends the second joint; which course allows to the sinew more liberty, and a more commodious action than it would other wise have been capable of exerting. There is Ches. Anat. p. 119. Bishop Wilkins hath observed from Galen, that there are, at least, ten several qualifications to be attended to in each particular mus. cle; viz. its proper figure; its just magnitude; its fulcrum; its point of action, supposing the figure to be fixed; its collocation, with respect to its two ends, the upper and the lower; the place; the position of the whole muscle; the introduction into it of nerves, arteries, veins. How are things, including so many adjust This system presents itself under two views : first, the disposition of the blood-vessels, i. e. the laying of the pipes; and, secondly, the construction of the engine at the centre, viz. the heart, for driving the blood through them. ments, to be made; or, when made, how are ing the waste, and of supplying an accession of they to be put together, without intelligence? substance to every part of a complicated maI have sometimes wondered, why we are not chine, at the same time. struck with mechanism in animal bodies, as readily and as strongly as we are struck with it, at first sight, in a watch or a mill. One reason of the difference may be, that animal bodies are, in a great measure, made up of soft, flabby substances, such as muscles and membranes; whereas we have been accustomed to trace mechanism in sharp lines, in the configuration of hard materials, in the moulding, chiseling, and filing into shapes, of such articles as metals or wood. There is something therefore of habit in the case; but it is sufficiently evident, that there can be no proper reason for any distinction of the sort. Mechanism may be displayed in the one kind of subtance, as well as in the other. I. The disposition of the blood-vessels, as far as regards the supply of the body, is like that of the water-pipes in a city, viz. large and main trunks branching off by smaller pipes (and these again by still narrower tubes) in every direction, and towards every part in which the fluid, which they convey, can be wanted. So far the water-pipes which serve a town may represent the vessels which carry the blood from the heart. But there is another thing necessary to the blood, which is not wanted Although the few instances we have select- for the water; and that is, the carrying of it ed, even as they stand in our description, are back again to its source. For this office, a renothing short perhaps of logical proofs of de-versed system of vessels is prepared, which, sign, yet it must not be forgotten, that in eve- uniting at their extremities with the extremiry part of anatomy, description is a poor sub-ties of the first system, collects the divided and stitute for inspection. It is well said by an subdivided streamlets, first by capillary rami. able anatomist, and said in reference to the fications into larger branches, secondly, by these very part of the subject which we have been branches into trunks; and thus returns the treating of: "Imperfecta hæc musculorum des- blood (almost exactly inverting the order in criptio, non minùs arida est legentibus, quàm which it went out) to the fountain whence its inspectantibus fuerit jucunda eorundem præ- motion proceeded. All which is evident me◄ paratio. Elegantissima enim mechanicês arti-chanism. ficia, creberrimè in illis obvia, verbis nonnisi The body, therefore, contains two systems obscurè exprimuntur: carnium autem ductu, of blood-vessels, arteries, and veins. Between tendinum colore, insertionum proportione, et the constitution of the systems there are also trochlearium distributione, oculis exposita, om-two differences, suited to the functions which nem superant admirationem." CHAPTER X. OF THE VESSELS OF ANIMAL BODIES. the systems have to execute. The blood, in going out, passing always from wider into nar. rower tubes; and, in coming back, from narrower into wider; it is evident, that the im pulse and pressure upon the sides of the bloodvessel will be much greater in one case than the other. Accordingly, the arteries which car. ry out the blood, are formed of much tougher THE circulation of the blood, through the bo and stronger coats, than the veins which bring dies of men and quadrupeds, and the apparait back. That is one difference: the other is tus by which it is carried on, compose a system, and testify a contrivance, perhaps the best ununderstood of any part of the animal frame. The lymphatic system, or the nervous system, may be more subtle and intricate; nay, it is possible that in their structure they may be even more artificial than the sanguiferous; but we do not know so much about them. still more artificial, or, if I may so speak, indicates, still more clearly, the care and anxiety of the artificer. Forasmuch as in the arteries, by reason of the greater force with which the blood is urged along them, a wound or rupture, would be more dangerous than in the veins, these vessels are defended from injury, not only by their texture, but by their situation; and The utility of the circulation of the blood, I by every advantage of situation which can be assume as an acknowledged point. One grand given to them. They are buried in sinuses, or purpose is plainly answered by it; the distri- they creep along grooves, made for them in buting to every part, every extremity, every the bones: for instance, the under-edge of the nook and corner of the body, the nourishment ribs is sloped and furrowed solely for the paswhich is received into it by one aperture.-sage of these vessels. Sometimes they proceed What enters at the mouth, finds its way to in channels, protected by stout parapets on the fingers' ends. A more difficult mechani- each side; which last description is remarkcal problem could hardly, I think, be proposed,able in the bones of the fingers, these being holthan to discover a method of constantly repair-lowed out, on the under-side, like a scoop, and with such a concavity, that the finger may be cut across to the bone, without hurting the ☛ Steno, in Blas. Anat. Animal. p. 2, o. 4. |