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."

36 When our author describes the variety of functions performed by the mouth and tongue, he is in admiration. at the simplicity of the instrument. But this is only an apparent simplicity: the complexity of structure is concealed. Indeed, it has been this very consideration which led to the new investigations into the nervous system. Without entering far into this subject, we take the tongue in illustration. It is a fine organ of touch: it is the seat of the sense of taste: it is necessary to deglutition: its modulations are infinite in speech; but the reason of a body so simple in its outward form being capable of performing offices apparently so discordant, is visible only to the anatomist, who traces the nerves into this organ, Then he discovers, besides the nerve proceeding from the papilla of the tongue to the sensorium, that there are nerves of volition governing the muscles of the tongue. In addition to these, there is a nerve which regulates the action of swallowing, and

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 species 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 ten

which combines the motions of the gullet with those of the tongue; and in the same manner another nerve, tending to the organ of voice in the larynx, branches off to the tongue, and associates it with the organ of the voice, so as to produce articulate language: these nervous cords are the true organization by which one member, simple in its exterior form, has a complexity in its internal relations. And thus it is, that in many instances organs which are apparently simple, and through which we perform many offices so easily that we think not at all of what is necessary to their execution, have yet internally, and to the eye of the anatomist, a thousand minute circumstances or relations on which the perfection of their action depends.

dons 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 tendinous contractions, definite, both as to the choice of the tendon, and as to the space through which the contraction 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.

II. Regarding the particular configuration of muscles, sphincter or circular muscles appear to be admirable pieces of mechanism. It is the muscular power most happily applied; the same quality of the muscular 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 semivoluntary 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 contraction 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 it.

IV. Mr. Home has observed,* that the most important and the most delicate actions are performed in the body by the smallest muscles; and he mentions, 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 are they 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.

[The figure here represents the action of the biceps muscle which lies on the arm, and is inserted upon the radius of the fore-arm in sustaining a weight in the hand.]

V. The muscles act in the limbs with what is called a mechanical disadvantage. The muscle at the shoulder, by which the arm is raised, is fixed nearly in the same manner as the load is

* Phil. Trans. part i. 1800, p. 8.