to point out instances in which, and properties with respect to which, the disposition of these muscles is as strictly mechanical, as that of the wires and strings of a puppet.*

I. We may observe, what I believe is universal, an ex act relation between the joint and the muscles which move it. Whatever motion the joint, by its mechanical construction, is capable of performing, that motion, the annexed muscles, by their positich, are capable of producing. For example; if there be, as at the knee and elbow, a hingejoint, capable of motion only in the same plane, the leaders, as they are called, i. e. the muscular tendons, are placed in directions parallel to the bone, so as, by the contraction or relaxation of the muscles to which they belong, to produce that motion and no other. If these joints were capable of a freer motion, there are no muscles to produce it. Whereas at the shoulder and the hip, where the ball and socket joint allows by its construction of a rotatory or sweeping motion, tendons are placed in such a position, and pull in such a direction, as to produce the motion of which the joint admits. For instance, the sartorius or tailor's muscle, rising from the spine, running diagonally across the thigh, and taking hold of the inside of the main bone of the leg, a little below the knee, enables us, by its contraction, to throw one leg and thigh over the other; giving effect, at the same time, to the ball and socket joint at the hip, and the hinge-joint at the knee. (Pl. XII. fig. 1.]

There is, as we have seen, a specific mechanism in the bones, for the rotatory motions of the head and hands; there is, also, in the oblique direction of the muscles belonging to them, a specific provision for the putting of this mechanism of the bones into action. [Pl. XII. fig. 2.] And mark the consent of uses. The oblique muscles would have been inefficient without that particular articulation; that particular articulation would have been lost, without the oblique muscles. It may be proper, however, to observe with respect to the head, although I think it does not vary the case, that its oblique motions and inclinations are ften motions in a diagonal, produced by the joint action of mus

* Muscles are the fleshy parts of the body which surround the bones, having a fibrous texture; a muscle being composed of a number of muscular faciculi, which are composed of fibres still smaller; these result from fibres of a less volume, until by successive division we arrive at very small fibres no longer divisible. These muscular fibres are longer or shorter according to the muscles to which they belong; an i every fibre is fixed by its two extremities to tendon or aponeurosis, which are the “wires and strings" which conduct the muscular power wher they contract.-Paxton.

cles lying in straight direction. But whether the pull be single or combined, the articulation is always such, as to be capable of obeying the action of the muscles. The oblique muscles attached to the head, are likewise so disposed, as to be capable of the steadying the globe, as well as of moving it. The head of a new-born infant is often obliged to be filleted up. After death, the head drops and rolls in every direction.

So that it is by the equilibre of the mus, cles, by the aid of a considerable and equipollent muscular force in constant exertion, that the head maintains its erect posture. The muscles here supply what would otherwise be a great defect in the articulation; for the joint in the neck, although admirably adapted to the motion of the head, is insufficient for its support. It is not only by the means of a most curious structure of the bones that a man turns his head, but by virtue of an adjusted muscular power, that he even holds it up.

As another example of what we are illustrating, viz. conformity of use between the bones and the muscles, it has been observed of the different vertebræ, that their processes are exactly proportioned to the quantity of motion which the other bones allow of, and which the respective muscles are capable of producing.

II. A muscle acts only by contraction. Its force is exerted in no other way.

When the exertion ceases, it relaxes itself, that is, it returns by relaxation to its former state; but without energy. This is the nature of the muscular fibre: and being so, it is evident that the reciprocal energetic motion of the limbs, by which we mean motion with force in opposite directions, can only be produced by the instrumentality of opposite or antagonist muscles; of flexors and extensors answering to each other. For instance, the biceps and brachiæus internus muscles, placed in the front part of the upper arm, by their contraction bend the elbow; and with such degree of force, as the case requires, or the strength admits of. [Pl. XIII. fig. 1.] The relaxation of these muscles, after the effort, would merely let the forearm drop down. For the back stroke, therefore, and that the arm may not only bend at the elbow, but also extend and straighten itself, with force, other muscles, the longus and brevis brachiæus externus, and the anconæus, placed on the hinder part or he arms, by their contractile twitch fetch back the fore-arm into a straight line with the cubit, with no les: force than that with which it was bent out of it The same thing obtains in all the limbs, and in every mov able part of the body. A finger is not bent and straighten.

ed, without the contraction ostwo muscles taking place. It is evident, therefore, that the animal functions require that particular disposition of the muscles which we describe by the name of antagonist muscles. And they are accordingly so disposed. Every muscle is provided with an adversary. They act, like two sawyers in a pit by an opposite pull; and nothing surely can more strongly indicate design and attention to an end, than their being thus stationed; than this collocation. The nature of the muscular fibre being what it is, the purposes of the animal could be answered by no other. And not only the capacity for motion, but the aspect and symmetry of the body, is preserved by the muscles being marshalled according to this order, e. g. the mouth is holden in the middle of the face, and its angles kept in a state of exact correspondency, by several mi scles drawing against, and balancing each other. (See Pl. XI .fig. 3.] In a hemiplegia, when the muscles on one side are weakened, the muscles on the other side draw the mouth awry.

III. Another property of the muscles, which could only be the result of care, is, their being almost universally so disposed, as not to obstruct or interfere with one another's action. I know but one instance in which this impediment is perceived. We cannot easily swallow whilst we gape. This, I understand, is owing to the muscles employed in the act of deglutition, being so implicated with the muscles of the lower jaw, that, whilst these last are contracted, the former cannot act with freedom. The obstruction is, in this instance, attended with little inconveniency; but it shows what the effect is where it does exist; and what loss of faculty there would be if it were more frequent. Now, when we reflect upon the number of muscles, not fewer than four hundred and forty-six in the human body, known and named,* how contiguous they lie to each other, in layers, as it were, over one another, crossing one another, sometimes embedded in one another; sometimes perforating one another; an arrangement, which leaves to each its liberty, and its full play, must necessarily require meditation and counsel

IV. The following is oftentimes the case with the muscles. Their action is wanted, where thei“ situation would be inconvenient. In which case, the body of the muscle is placed in some commodious position at a distance, and inade to communicate with the point of action, by slender

* Keill's Anat. p. 295, edit. 3. There are, however, five hundred and i venty-seven mussles described by more modern anatomists.


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. [Pl. XIII. fig. 1, 2.] 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, (Pl. IV. fig. 2, 3,) and where it encumbers nothing.*

V. The great mechanical variety in the figure of the muscles may be thus stated. It appears to be a fixed law, that the contraction of a muscle shall be towards its centre. Therefore, the subject for mechanism on each occasion is, so to modify the figure, and adjust the position of the muscle, as to produce the motion required, agreeably with this law. This can only be done by giving to different muscles 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, 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

* The convenience and beauty of the tendons seem only an ulterior ob'ect, their necessity and utility principally claim our attention. The fone which a muscle possesses is as the number of the muscular fibres; but a limited numb or of fibres only can be fixed to any certain point of bone destined to be hoved, therefore the contrivance is, to attach them to a cord, called a sir.ew or tendon, which can be conveniently conducted and fixed to the bone. If we are desirous of moving a heavy weight, we tie a strong cord to it, that a greater number of men may apply their strength. Thus a similar effect is produced--the muscular fibres are the moving powers, the teridons are the cords attached to the point to be moved.-Paxton.

[merged small][ocr errors]

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 intended.

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, to be vigorous and active! Yet vigor 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 not withstanding that the defect or disorder sometimes of a very small instrument, of a single pair, for instance, out of tho 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, [Pl. XIV. fig. 1, 2,] 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, how little those who enjoy the perfect use of their organs, know the comprehensiveness of the blessing, thc variety of their obligation. They perceive a result, but they think little of the multitude of concurrences and rectitudes which


to form it. Besides these observations, which belong to the muscular organ as such, we may notice some advantages of structure, which are more conspicuous in muscles of a certain class or description than in others. Thus:

I. The variety, quickness, and precision, of which muscular motion is capable, are seen, I think, in no part so remarkable 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, porceptible to the sight, insomuch, that curious

« VorigeDoorgaan »