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 articulate sound correctly. How instantaneously are these positions assumed and dismissed! how numerous are the permutations, how various, yet how infallible! Arbitrary and antic variety is not the thing we admire; but variety obeying a rule, conducing to an effect, and commensurate with exigencies infinitely diversified. I believe also that the anatomy of the tongue corresponds with these observations upon its activity. The muscles of the tongue are so numerous and so implicated with one another, that they cannot be traced by the nicest dissection; nevertheless (which is a great perfection of the organ,) neither the number, nor the complexity, nor what might seem to be the entanglement of its fibres, in anywise impede its motion, or render the determination or success of its efforts uncertain.

I here entreat the reader's permission to step a little out of my way, to consider the parts of the mouth, in some of their other properties. It has been said, and that by an eminent physiologist, that, whenever nature attempts to work two or more purposes by one instrument, she does both or all imperfectly. Is this true of the tongue, regarded as an instrument of speech, and of taste; or regarded as an instrument of speech, of taste and of deglutition? So much otherwise, that many persons, that is to say, nine hundred and ninety-nine persons out of a thousand, by the instrumentality of this one organ, talk, and taste, and swallow, very well. In fact, the constant warmth and moisture of the tongue, the thinness of the skin, the papillæ upon its surface, qualify this organ for its office of tasting, as much as its inextricable multiplicity of fibres do for the rapid movements which are necessary to speech. Animals which feed upon grass, have their tongues covered with a perforated skin, so as to admit the dissolved food to the papillæ underneath, which, in the meantime, remain defended from the rough action of the unbruised spicule.*

Papillæ are small bodies situated on the surface and sides of the tongue; they are furnished by the extreme filaments of the gustatory nerve, through which medium we acquire the sense of tasting. In her nivorous animals the papillæ are sharp pointed and directed backwards o assist in laying hold of the grass. In the cat kind there is a horny or prickly set covering the tongue, rendering it rough, and enabling it to

There are brought together within the cavity of the mouth more distinct uses, and parts executing more distinct offices, than I think can be found lying so ear to one another, or within the same compass, in any other portion of the body: viz. teeth of different shape,* first for cutting; secondly for grinding: muscles, most artificially disposed for carrying on the compound motion of the lower jaw, half lateral and half vertical, by which the mill is worked: fountains of saliva, springing up in different parts of the cavity for the moistening of the food, whilst the mastication is going on: glands,† to feed the fountains; a muscular constriction of a very peculiar kind in the back part of the cavity, for the guiding of the prepared aliment into its passage towards the stomach, and in many cases for carrying it along that passage; for, although we may imagine this to be done simply by the weight of the food itself, it in truth is not so, even in the upright posture of the human neck; and most evidently is not the case with quadrupeds, with a horse for instance, in which, when. pasturing, the food is thrust upward by muscular strength, instead of descending of its own accord.

In the meantime, and within the same cavity, is going on another business, altogether different from what is here described, that of respiration and speech. In addition therefore, to all that has been mentioned, we have a passage opened, from this cavity to the lungs, for the admission of air, exclusively of every other substance; we have muscles, some in the larynx, and without number in the tongue, for the purpose of modulating that air in its passage, with a variety, a compass, and precision, of which no other musical instrument is capable. And, lastly, which in my opinion crowns the whole as a piece of machinery, we have a specific contrivance for dividing the pneumatic part from

take firmer hold of the prey. Birds also have a similar contrivance. In fish the tongue is covered by a number of teeth, serving the same purpose.

Paxton.

* In each jaw there are four incisores, or cutting teeth, two canine which may be ranked with the former, only more pointed; four small molar, and six large molar or grinding teeth. And as the teeth of animals indicate the food on which they are destined to subsist, so from analogy we may infer that man is called to use either animal or vegetable aliments, or both, i. e. keeps a mean between graminivorous and carnivorous animals, in the structure and complication of his digestive apparatus, without deserving on that account to be called omnivorous: for it is known, that, a great number of the substances upon which animals feed are of no use in the support of man.---. Paxton.

The principal of these are the parotids, see Plate XX.

the mechanical, and for preventing one set of actions in terfering with the other. Where various functions are united, the difficulty is to guard against the inconveniences of a too great complexity. In no apparatus put together by art, and for the purposes of art, do I know such multifarious uses so aptly combined, as in the natural organization of the human mouth; or, where the structure, compared with the uses, is so simple. The mouth, with all these intentions to serve, is a single cavity; is one machine, with its parts neither crowded nor confused, and each unembarrassed by the rest: each at least at liberty in a degree sufficient for the end to be attained. If we cannot eat and sing at the same moment, we can eat one moment, and sing the next: the respiration proceeding freely all the while.

There is one case, however, of this double office, and that of the earliest necessity, which the mouth alone could not perform; and that is, carrying on together the two actions of sucking and breathing. Another route, therefore, is opened for the air, namely, through the nose, which lets the breath pass backward and forward, whilst the lips, in the act of sucking, are necessarily shut close upon the body from which the nutriment is drawn. This is a circumstance which always appeared to me worthy of notice. The nose would have been necessary, although it had not been the organ of smelling. The making it the seat of a sense, was superadding a new use to a part already wanted; was taking a wise advantage of an antecedent and a constitutional necessity.

But to return to that which is the proper subject of the present section-the celerity and precision of muscular motion. These qualities may be particularly observed in the execution of many pieces of instrumental music, in which the changes produced by the hand of the musician are exceedingly rapid; are exactly measured, even when most minute; and display, on the part of the muscles, an obedience of action, alike wonderful for its quickness and its

correctness.

Or let a person only observe his own hand whilst he is writing; the number of muscles which are brought to bear upon the pen: how the joint and adjusted operation of several tendons is concerned in every stroke, yet that five hundred such strokes are drawn in a minute. Not a letter can be turned without more than one, or two, or three ter dinoustractions, definite, both as to the choice of

the tendon, and as to the space through which the retraction 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 endeavou or habit hath inculcated! For let it be remembered, tha 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 do cility.

II. Regarding the particular configuration of muscles, sphincter or circular muscles appear to me admirable pieces of mechanism. [Pl. XIV. fig. 3.] It is the muscular power most happily applied; the same quality of the musculai substance, but under a new modification. The circular disposition 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 contraction, 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 semi-voluntary character, is exactly such as suits with the wants and functions of the animal.

III. We may also, upon the subject of muscles, observe, that many of our most important actions are achieved by the combined help of different muscles. Frequently, a diagonal motion is produced by the retraction of tendons pulling in the direction of the sides of the parallelogram. This is the case, as hath been already noticed, with some of the oblique nutations of the head. Sometimes the number of co-operating muscles is very great. Dr. Nieuentyt, in the Leipsic Transactions, reckons up a hundred muscles that are employed every time we breathe; yet we take in, or let out, our breath, without reflecting what a work is thereby performed; what an apparatus is laid in, of instruments for the service, and how many such contribute their assistance to the effect! Breathing with ease, is a blessing of every moment; yet, of all others, it is that which we possess with the least consciousness. A man in an asthma is the only man who knows how to estimate t.

IV. Sir Everard Home has observed,* that the most important and the most delicate actions are performed in the

*Phil. Trans. part 1. 1800. p 8

body by the smallest muscles; and he mentiras, as his examples, the muscles which have been discovered in the iris of the eye, and the drum of the ear. The tenuity of these muscles is astonishing. They are microscopic hairs; must be magnified to be visible; yet they are real, effective muscles; and not only such, but the grandest and most precious of our faculties, sight and hearing, depend upon their health and action.

V. The muscles act in the limbs with what is called a mechanical disadvantage. The muscle at the shoulder, [PI. XIII. fig. 1. f.] 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 centre, and on the other side of it. And this is the disadvantage which is meant. And an absolute disadvantage, no doubt, would be, if the object were to spare the force of muscuar contraction. But observe how conducive is this consti.. tution to animal conveniency. 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 light weight rapidly, through a considerable sweep. For the former of these purposes, a different species of lever, and a different collocation of the muscles, might be better than the present; but for the second, the present structure is the true one. Now so it happens, 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 be able to carry his hand to his head with due expedition, than it would be to have the power of raising from the ground a heavier load (of two or three more hundred weight, we will suppose,) than he can lift at present. This last is a faculty, which on some extraordinary occasions he may desire to possess, but the other is what he wants, and uses every hour and minute. In like manner, a husbandman, or a gardener, will do more execution, by being able to carry his scythe, his rake, or his flail, with a sufficient despatch through a sufficient space, than if, with greater strength, his motions were proportionably more confined and slow. It is the same with a mechanic in the use of his tools. It is the same also with other animals in the use of their limbs.

In