MIOLOOT.
Muscles consist of bundles of red fibres; but the colour is not essential, since it can be removed by repeated wa.shings and maceration.
The threads composing a muscle tu-e enveloped by cellular substance, which connects it to the surrounding parts. Each bundle consists of numerous fibres, vf small, that our instruments of research cannot arrive at the ultimate or original fibre : hence, any perceivable fibre, how ever small, is formed by the juxta-position of ntunerous fibrillz ; and, as we employ magnifying instruments of greater power, a fibre, which before seemed simple, re solves itself into a congeries of still more minute threads. We pass over in silence the dreams of various investigators, who have busied themselves in looking for the ultimate muscular fibre ; these researches do not assist us in explaining the pheno mena of muscular action. The cohesion of the constituent particles of the moving fibre is maintained by the vital power : hence, a dead muscle will be torn by a weight of a few ounces, which in the living body would have supported many pounds. The muscular fibre receives a copious supply of vessels and nerves. ' Tendons are formed bv an assemblage of longitudinal parallel fibres. They are extremely dense andtough, of a splendid white colour, which is beautifully con trasted with the florid red of a healthy muscle. The muscular fibres terminate in these bodies, and they are connected to the hones. They possess no apparent nerves, and very few and small blood vessels.
There is always an exact relation be tween tile joint and the n luscles that move it. 1Vhatever mot/on tbe joint, by its me chanical construction, i3 capable of per forming, tfiAt motion the annexed muscles, by thel: position, are capable of produc ing. For example, if there be, as at the knee and elbow, a hinge joint, capable of motion only in the same plane, the muscles and tendons are placed in directions pa rallel to the bone, so as by their construe tion to produce that motion, and no other. If these joints were capable of freer motion, there are no muscles to produce it. Whereas, at the shoulderand the hip, where the ball and socket joint allows by its construction a rotatory or sweeping motion, tendons are placed in such a posi tion, and pull in such a direction, as to pro duce the motion of which the joint admits. In the head and hand, there is a specific mechanism in the bones for rotatory mo tion ; and there is accordingly, in the obli que direction of the ninnies belonging to them, a specific provision for putting this mechanism of the bones into action. The oblique muscles would have been ineffi cient without that particular articulation, fld tliat particulararticulation \rot t Id have been useless without the muscles.
As the muscles act only by contraction, it is evident that the reciprocal energetic motion-of the limbs, or their motion with force in opposite directions, can only be produced by the instrumentality of oppo site or antagonist muscles, of flexors and extensors answering to each other. For instance, the biceps and brachialis inter nus, placed in the front of the arm, hy their contraction, bend the elbow, and with such degree of force as the case re quires, or the strength admits of The relaxation of these muscles after the effort would merely let the fore-arm drop down: for the back stroke, therefore, and that the arm may not only bend at the elbow, but also extend and straigthen itself with force, other muscles, as the triceps and anconeus, placed on the hinder part of the arm, fetch back the fore-arm into a straight line with the humerus, with no less force than that with which it was bent out of it.
It is evident, therefore, that the animal functions require that particular disposi tion of the muscles which we call anta gonist muscles.
It often happens that the action of mus cl es i s wanted, where their situation would he inconvenient. In which case, the bo dy of the muscle is placed in some com modious position at a distance, and it com municates with the point of action by slender tendotss. If the muscles which move the fingers Uad been placed in the pabn or hack of the band, they would have swelled that part te. an awkward and clumsy thickness. The bsantv, the proportions of the part, would has s7 freen destroyed. They are therefore clispossrl in the arm, and even up to thc elbow, and act by long tendonsstrapped down at tbe wrist, and passing ender the ligament to the fingers, and to the joints of the fin gers, which they are severally to move. In the same manner the muscles, whith move the toes and many of thc joints of the foot, are gracefully disposed in the calf of the leg, instead of forming an un wieldy tumefaction in the foot itself The great mechanical variety in the figure of the muscles may be thus stated. It appears to be a fixed law, that the con traction of a muscle shall be towards its centre. Therefore the subject for me chanism on each occasion is, sato modify the figure, and adjust the position of the muscle, as to produce the motion requir ed, agreeably with this law. This can only be done by giving to different mus cles a diversity of configutution, suited to their several offices, and to their situa tion 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, some times with none ; sometimes obe tendon to several muscles, at other times one muscle to several tendons. The shape of the organ is 'susceptible of an incalcula ble 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 quality of his materials, or their laws of action. He takes these as he find-s them. His skill and ingenuity are employed in bulling 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.