general, the vivacity of their motions would be ill exchanged for greater force under a clumsier 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:

I. Of muscular actions, even of those which are well understood, some of the most curious are incapable of popular explanation; at least, without the aid of plates and figures.* This is in a great measure the case, with a very familiar, but, at the same time, a very complicated motion— that of the lower jaw; and with the muscular structure by which it is produced. One of the muscles concerned may, however, be described in such a manner, as to be, I think, sufficiently comprehended for our present purpose. The problem is to pull the lower jaw down. The obvious method should seem to be, to place a straight 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 some muscular mechanism disposed farther back in the jaw. The mechanism adopted is as follows: [Pl. XV. fig. 1, 2.] A certain muscle called the digastric, rises on the side of the face, considerably above the insertion of the lower jaw, and comes down, being converted in its progress into a round tendon. Now, it is evident, that the tendon, whilst it pursues a direction descending towards the jaw, must, by its contraction, pull the jaw up, instead of down. What then was to be done? This, we find is done: The descending tendon, when it is got low enough, is passed through a loop, or ring, or pulley, in the os hyoïdes, and then made to ascend: and, having thus changed its line of direction, is inserted into the inner part of the chin: by which device, viz. the turn at the loop, the action of the muscle (which in all muscles is contraction) that before would have pulled the jaw up, now as necessarily draws it down. "The mouth," says Heister, "is opened by means of this trochlea in a most wonderful and elegant manner. II. What contrivance can be more mechanical than * The want of the aid of plates and figures, which the author here expresses, is now supplied in this Boston edition.

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the following, viz. a slit in one tendon to let another teu don 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 otherwise have been capable of exerting.* [Pl. XVI. fig. 1, 2.] There is nothing, I believe, in a silk or cotton mill, in 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 evidently so, than this perforation.

III. The next circumstance which I shall mention, under this head of muscular arrangement, is so decisive a mark of intention, that it always appeared to me, to supersede, in some measure, the necessity of seeking for any other observation upon the subject; and that circumstance is, the tendons, which pass from the leg to the foot, being bound down by a ligament at the ankle. [Pl. XVI. fig. 3.] The foot is placed at a considerable angle with the leg It is manifest, therefore, that flexible strings, passing along the interior of the angle, if left to themselves, would, when stretched, start from it. The obvious preventive is to tic them down. And this is done in fact. Across the instep, or rather just above it, the anatomist finds a strong ligament under which the tendons pass to the foot. The ef fect 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 contrivance, its exact resemblance to established resources of art, place it amongst the most indubitable manifestations of design with which we are acquainted.

There is also a farther use to be made of the present example, and that is, as it precisely contradicts the opinion, that the parts of animals may have been all formed by what is called appetency, i. e. endeavour, perpetuated, and imperceptibly working its effect, through an incalculable series of generations. We have here no endeavour, but the reverse of it; a constant renitency and reluctance. The endeavour is all the other way. The pressure of the ligament constrains the tendons; the tendons react upon the pressure of the ligament. It is impossible that the ligament should ever have been generated by the exercise of the tendon, or in the course of that exercise, forasmuch as

* Ches. Anat. p. 94, 119.

the force of the tendon perpendicularly resists the fibre which confines it, and is constantly endeavouring, not to form, but to rupture and displace, the threads of which the ligament is composed.

Keill has reckoned up, in the human body, four hundred and forty-six muscles, [See note, p. 77,] dissectible and describable; and hath assigned a use to every one of the number. This cannot be all imagination.

Bishop Wilkins hath observed from Galen, that there are, at least, ten several qualifications to be attended to in each particular muscle; 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, and veins. How are things, including so many adjustments, to be made, or, when made, how are they to be put together, without intelligence?

I have sometimes wondered, why we are not 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 anima! 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, 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 one kind of substance, as well as in the other.

Although the few instances we have selected, even as they stand in our description, are nothing short perhaps of logical proofs of design, yet it must not be forgotten, that, in every part of anatomy, description is a poor substitute for inspection. It is well said by an able anatomist,* and said in reference to the very part of the subject which we have been treating of:-"Imperfecta hæc musculorum descriptio, non minùs arida est legentibus, quàm inspectantibus fuerit jucunda eorundem præparatio. Elegantissima enim mechanicês artificia, creberrimè in illis obvia, verbis nonnisi obscurè exprimuntur: carnium

*Sterno in Blas. Anat. Animal. p. 2. c 4.

autem ductu, tendinum colore, insertionum proportione, et trochlearium distributione, oculis exposita, omnen superant admirationem.”

The following remarks upon the structure of the tendons, from the Animal Mechanics already quoted, will form an instructive addition to the foregoing chapter, to the subject of which they bear a near relation.-Ed.

Of the Cordage of the Tendons.

Where nature has provided a perfect system of columns and levers, and pullies, we may anticipate that the cords by which the force of the muscles is concentrated on the movable bones, must be constructed with as curious a provision for their offices. In this surmise we shall not be disappointed.

To understand what is necessary to the strength of a rope or a cable, we must learn what has been the object of the improvements and patents in this manufacture. The first process in ropemaking, is hatchelling the hemp: that is, combing out the short fibres, and placing the long ones parallel to one another. The second is, spinning the hemp into yarns. And here the principle must be attended to, which goes through the whole process in forming a cable; which is that the fibres of the hemp shall bear an equal strain: and the difficulty may be easily conceived, since the twisting must derange the parallel position of the fibres. Each fibre, as it is twisted, ties the other fibres together, so as to form a continued line, and it bears, at the same time, a certain portion of the strain, and so each fibre alternately. The third step of the process is making the yarns. Warping the yarns, is stretching them to a certain length; and for the same reason, that so much attention has been paid to the arrangement of the fibres for the yarns, the same care is taken in the management of the yarns for the strands. The fourth step of the process is to form the strands into ropes. The difficulty of the art has been to make them bear alike, especially in great cables, and this has been the object of patent machinery. The hardening, by twisting, is also an essential part of the process of rope-making: for without this, it would be little better than extended parallel fibres of hemp. In this twisting, first of the yarns, and then of the strands, those which are on the outer surface must be more stretched than those near the centre; consequently, when there is a strain upon the rope, the outer fibres will break first, and the others in succession. It is to avoid this, that each yarn and each strand, as it is twisted or hardened, shall be itself revolving, so that when drawn into the cable, the whole component parts may, as nearly as possible, resist the strain in an equal degree; but the process is not perfect, and this we must conclude from observing how different the construction of a tendon is from that of a rope. A tendon consists of a strong cord, apparently fibrous; but which, by the art of the anatomist, may be separated to lesser cords, and these, by maceration, can be

shown to consist of cellular membrane, the common tissue that gives firmness to all the textures of the animal body. The peculiarity here results merely from its remarkable condensation. But the cords of which the larger tendons consists, do not lie parallel to each other, nor are they simply twisted like the strands of a rope; they are, on the contrary, plaited or interwoven together.

If the strong tendon of the heel, or Achilles tendon, be taken as an example, on first inspection, it appears to consist of parallel fibres, but by maceration, these fibres are found to be a web of twisted cellular texture. If you take your handkerchief, and, slightly twisting it, draw it out like a rope, it will seem to consist of parallel cords; such is, in fact, so far the structure of a tendon. But, as we have stated, there is something more admirable than this, for the tendon consists of subdivisions, which are like the strands of a rope; but instead of being twisted simply as by the process of hardening, they are plaited or interwoven in a way that could not be imitated in cordage by the turning of a wheel. Here then Is the difference-by the twisting of a rope, the strands cannot resist the strain equally, whilst we see that this is provided for in the tendon by the regular interweaving of the yarn, if we may so express it, so that every fibre deviates from the parallel line in the same degree, and, consequently, receives the same strain when the tendon is pulled. If we seek for examples illustrative of this structure of the tendons, we must turn to the subject of ship-rig ging, and see there how the seaman contrives, by undoing the strands and yarns of a rope, and twisting them anew, to make his splicing stronger than the original cordage. A sailor opens the ends of two ropes, and places the strand of one opposite and between the strand of another, and so interlaces them. And this explains why a hawser-rope, a sort of small cable, is spun of three strands; for as they are necessary for many operations in the rigging of a ship, they must be formed in a way that admits of being cutand spliced, for the separation of three strands, at least, is necessary for knotting, splicing, whipping, mailing, &c., which are a few of the many curious contrivances for joining the ends of ropes, and for strengthening them by filling up the interstices to preserve them from being cut or frayed. As these methods of splicing and plaiting in the subdivisions of the rope make an intertexture stronger than the original rope, it is an additional demonstration, if any were wanted, to show the perfection of the cordage of an animal machine, since the tendons are so interwoven; and until the yarns of one strand be separated and interwoven with the yarns of another strand, and this done with regular exchange, the most approved patent ropes must be inferior to the corresponding part of the animal machinery.

A piece of cord of a new patent has been shown to us, which is said to be many times stronger than any other cord of the same diameter. It is so far upon the principle here stated, that the strauds are plaited instead of being twisted; but the tendon has still its superiority, for the lesser yarns of each strand in it are interwoven with those of other strands. It however, gratifies us to see, that the principle we draw from the animal body is here con

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