Part 26

Their thickness is not great; most of them appear like muscular membranes, sometimes arranged in layers, as in the abdomen, sometimes covering the long muscles, as on the back; they are in the first case, much more extensive superficially than deeper seated.

Whenever abroad muscle arises and terminates on one of the great cavities, it preserves everywhere nearly its breadth, because it has a large surface for its insertion. But if from a cavity it goes to a long bone, or to a small apophysis, then its fibres gradually approximate; it loses its breadth, increases in thickness, and terminates in an angle which is succeeded by a tendon, which concentrates into a very small space fibres widely scattered on the side of the cavity. The great dorsal and pectoral muscles present us an example of this arrangement, which is met with also in the iliacus, in the glutæi medius and minimus. The broad muscles of the pectoral cavity have a peculiar arrangement which the ribs require; their origin takes place by serrated points fixed to these bones, and separated by spaces between them.

The broad muscles are most often simple; many rarely unite to form compound ones. Different cellular layers separate them, like the long muscles; but they are hardly ever like them covered by aponeuroses; the greatest number is merely subjacent to the integuments; the reason is that their form naturally protects them from these displacements, of which we have spoken in the article on aponeuroses, and which, without these membranes, would be so frequent in the long muscles. I do not know that the cramp has ever been observed in those of which we are treating. When the abdominal muscles are laid bare by incisions made through the integuments of a living animal, I have observed, that in contracting, the bulk of each preserves the same place.

III. _Forms of the Short Muscles._

The short muscles are those in which the three dimensions are nearly equal, having a thickness in proportion to their width and their length. They are found in general in the places, where is required on the one hand much power, and on the other small extent of motion; thus around the temporo-maxillary articulation the masseter and pterygoids, around the ischio-femoral the quadratus the gemini the obturators, &c. around the scapulo-humeral the supra-spinalis and the teres minor, in the hand the muscles of the palmar eminences, in the foot various fleshy fasciculi, in the vertebral column the interspinal, in the head the small and great anterior, posterior and lateral recti, exhibit more or less regularly the form of which we are treating, and answer the double object that I have indicated, on the one hand by the very considerable number and on the other by the shortness of their fibres.

The short muscles are, more often than the broad, united to each other, either in their origin or termination, as we see in the foot and the hand. Sometimes they are of a triangular form, as in these two parts; sometimes they approach to the form of a cube, of which there is an example in the masseter and pterygoid muscles. In general they are rarely covered by aponeuroses, undoubtedly because the shortness of their fibres prevents them from being liable in a great degree to considerable displacements.

Besides, the division of the muscles into long, broad and short, is, like that of the bones, subject to an infinite number of modifications. In fact many of these organs have mixed characters; thus the sub-scapularis and the infra-spinalis have a form intermediate to the broad and short one; thus the cruræus, the gemelli of the leg, &c. cannot be considered precisely long or broad muscles. Nature varies, according to the functions of the organs, the conformation of the agents of their motions, and we can only establish approximations in our anatomical divisions.

ARTICLE SECOND.

ORGANIZATION OF THE MUSCULAR SYSTEM OF ANIMAL LIFE.

The part peculiar to a muscle is what is commonly called the muscular fibre; the vessels, the nerves, the exhalants, the absorbents and the cellular texture, which is very abundant around this fibre, form its common parts.

I. _Texture peculiar to the Organization of the Muscular System of Animal Life._

The muscular fibre is red, soft, of an uniform size in the great and small muscles, sometimes disposed in very evident fasciculi and separated from each other by remarkable grooves, as in the gluteus maximus, the deltoid, &c. sometimes more equally in juxta-position, as in most of the broad muscles, always united to many others of the same nature like it, easily by this union distinguished by the naked eye, but eluding microscopic researches when we wish to examine it in a separate manner, so great is its tenuity. Notwithstanding this extreme tenuity, an infinite number of researches have been made during the last age, to determine with precision the size of this fibre. On this point may be read the result of the labours of Leuwenhoek, Muysk, &c. I shall not give here this result, because science can draw nothing from it, and because we cannot rely upon its accuracy; of what importance moreover is the precise size of the muscular fibre? its knowledge would add nothing to our physiological views upon the motion of the muscles.

Every muscular fibre runs its course without bifurcating or dividing in any manner, though many have thought otherwise; it is found only in juxta-position to those which are near it, and not intermixed, as often happens in the fibrous system; an arrangement that was rendered necessary by the insulated motions it performs; for the general contraction of a muscle is the union of many partial contractions, wholly distinct and independent of each other.

The length of the fleshy fibres varies very much. If we examine in general the mass which they form by their union, we observe that this mass has sometimes much greater extent than the tendinous portion of the muscle, as the biceps, the coraco-brachialis, the rectus internus femoris, &c.; that sometimes its length is much less as in the small plantar and palmar muscles, &c.; and that sometimes it is about equal, as in the external radial, &c. If from the examination of the fleshy mass, we pass to that of the separate fibres that compose it, we see that the length of the first is rarely the same as that of the second. There are hardly any but the sartorius and some analogous muscles, whose fibres run the whole extent of the fleshy, mass; in almost all the others, they are found obliquely arranged between two aponeuroses, or between a tendon and an aponeurosis; so that though each of them may be very short, as a whole they are very long, as we observe in the anterior rectus of the thigh, the semi-membranosus, &c. This arrangement may also arise from various tendinous intersections, which cut at different distances the length of the fibres. In general, the muscles which owe their length to long fibres, have great extent and very little power of motion; whilst those with short fibres, but multiplied so as to give great length as a whole, are remarkable for an opposite character. And this is the reason: all the fibres being equally large, whatever may be their length, have the same degree of force; it is evident then that this force considered in a muscle as a whole, is measured by the number of its fibres. On the other hand, the longer a fibre is, the more it shortens in its contraction; then by contracting, a muscle brings its attachments so much the nearer in proportion as its fibres are longer.

All the fibres of the voluntary muscles are straight, those of the sphincters excepted. They are either parallel as in the rhomboids, or obliquely situated in relation to each other, as in the great pectoral. Sometimes in the same muscle many sets cross each other in different directions, as we see in the masseter; but this crossing is wholly different from that of the involuntary muscles in which there is more crossing of fibres, whilst here we see only fasciculi in different directions, in juxta-position to each other.

I shall not speak here of the cylindrical form according to some, and the globular one according to others, of the fleshy fibre; inspection teaches us nothing upon this point; how then can we make that an object of research and give an opinion upon it, which has no real foundation? Let us say thus much of the intimate nature of this fibre, upon which so much has been written. It is unknown to us, and all that has been said upon its continuity with the vascular and nervous extremities, upon its pretended cavity, upon the marrow, which according to some filled it, &c. is only a collection of vague ideas, which nothing positive confirms, and to which a methodical mind would not attend. Let us begin to study nature where she begins to come under our senses. I would compare the anatomical researches upon the intimate structure of the organs, to the physiological researches upon the first causes of the functions. In both we are without guides, without precise and accurate data; why then give ourselves up to them?

All that we can know upon the nature of the muscular fibre, is that it is peculiar, that it is not the same as that of the nerves, nor as that of the vessels, nor as that of the tendons or the cellular texture; for where there is identity of nature, there ought to be identity of vital properties and of texture. Now we shall see that all these systems differ essentially from each other in this point of view; there can be between them no analogy in relation to their nature, whence the properties are always derived.

The muscular texture is remarkable for its softness and small degree of resistance. It is by this that it is essentially different from the fibrous texture. It breaks with ease in the dead body. In the living, this rupture is rare, because the contraction which exists in all the violent efforts, gives it a density, by which it gains an enormous increase of resistance, but which it loses when it is no longer in a state of contraction. There are however examples of the rupture of muscles; it is principally in the rectus abdominis and quadratus lumborum that they take place. I have seen one in this last. Observe that this muscle and all those placed between the ribs and the pelvis, are much disposed, from their situation, to these ruptures. In fact, when the pelvis and the thorax are carried in an opposite direction, these muscles are so much the more violently stretched, as in these motions all the superior part of the body forms with the thorax, a great lever, which is moved in an opposite direction to another great lever, which is formed by the pelvis and all the inferior parts; now from their length, these levers are capable of receiving a very great motion, of communicating it consequently to the abdominal muscles which are stretched between the two, and which serve to unite them. Hence how in a violent inclination to the right, the quadratus of the left side can be torn, &c. Observe that but few of the muscles in the economy are found between two levers so great, consequently are capable of being so much distended, and especially of being so with a force greater than that of their contraction; for every muscular rupture supposes the excess of the external motion, which distends, over that of the fleshy fibres which contract to oppose this distension. If the external efforts were concentrated upon a single muscle, they would be able more often to overcome the resistance; but almost always many partake of the effort to support and the resistance to oppose.

_Composition of the Muscular Texture._

The muscular texture has been with chemists, a more particular object of research than most of the other organized textures. They have examined it under all its relations. I refer to their works, to that of Fourcroy especially, for all which is not strictly relative to the nature of this texture, for all which considers consequences not applicable to physiology, which we can deduce from the knowledge of the principles that enter into its composition.

Exposed to the action of the air, the muscular texture is affected in two ways. 1st. It dries, if cut into thin slices, admitting of the evaporation of the fluids it contains. Then its appearance is of a dull brown; its fibres contract, it becomes thinner, hard and brittle. If replunged into water within some days, even fifteen or thirty after its drying, it resumes its primitive softness and form, and has a less deep coloured tinge. The water that has been used for this softening is more or less fetid, and similar to that of macerations. 2d. Exposed in too great a mass to the air, the muscular texture does not dry, but becomes putrid. Thus in making anatomical preparations by drying, care should be taken to lessen the thickness of the fleshy parts, or to arrange them so that the air can penetrate them everywhere. Putrefaction is inevitable if the air is moist, if the evaporation of the fluids is not quick enough to produce drying. When it becomes putrid, the muscle assumes a green, livid colour; it exhales an offensive odour. Under the influence of the same circumstances it becomes putrid much quicker than the fibrous, the cartilaginous and the fibro-cartilaginous systems. The odour that it exhales then is also very different from that of these systems; a phosphoric light often escapes from it. A mass of putridity, in which all the fibres have almost disappeared, takes the place of the muscle, when putrefaction is advanced. This mass of putridity gradually evaporates in part, and there remains a dark brown residue, which dries and becomes hard and brittle, nearly like the muscle dried in the ordinary state, though the appearance however may be very different.

Exposed to the action of water, the muscle undergoes different phenomena, according as it is hot or cold. Cold water takes from it at first its red colour, of which it appears to dissolve the principle. To effect quickly this phenomenon, it is necessary to expose the flesh, at first in thin layers, to the action of water that is often changed, by placing a muscle for example under a fountain, in the current of a river, or what is much better, by frequently expressing the water it imbibes; for if we keep it in a vessel, its exterior only whitens a little, and the interior preserves its colour. Water which has been used to wash a muscle, looks like blood spread out in this fluid; it contains the colouring matter, a little of the extractive substance, gelatine, &c. I believe that of all the organs the muscle is that from which we remove most easily its colour by artificial means. Ought we to be astonished after this, if nature varies so evidently and so frequently this colour by the phenomena of nutrition, as we soon shall have occasion to remark? Kept in water at a moderate temperature, the muscular texture remains for a long time without softening; it finally does, and changes layer by layer into a kind of putridity very different however from that which is formed in the open air, as I have frequently observed in macerating the muscles in a cellar, the temperature of which is uniform. At other times, instead of putrefying thus, the muscle is changed, as Fourcroy has remarked, into a substance like spermaceti; then its fibre is hard and solid. But all the muscles when kept in water by no means exhibit this phenomenon. When it does take place, very often a kind of reddish product, scattered here and there on the surface of the muscle, and which is an evident effect of decomposition, announces and afterwards accompanies this state, without which also, it often takes place. Maceration in dissecting rooms frequently exhibits this phenomenon.

When we have taken from the muscles their colouring substance by repeated washings, there remains a white fibrous texture, from which we can still extract albumen by ebullition, which rises in scum, gelatine by suffering it to grow cold, extractive matter which has a deep colour, by letting it settle, and some phosphoric salts. When all these substances have disappeared, the residue of the muscle is a fibrous substance, of a greyish colour, insoluble in warm water, soluble in the weak acids, giving out much azote from the action of the nitric acid, and presenting all the characters of the fibrin of the blood. It appears, as Fourcroy has remarked, that this substance is truly the nutritive substance of the muscle, that which, continually exhaled and absorbed, contributes to its nutritive phenomena more than all the others; it constitutes the essence of the muscle, it especially characterizes it, as the phosphate of lime is the nutritive characteristic matter of the bones. Is this substance formed in the blood and carried from it to the muscle, or is it formed in the muscle by nutrition, and thence carried to the blood? I know not. Whichever may be the case, it appears to experience very great varieties in its exhalation and absorption. The state of laxity, of cohesion, the thousand various appearances of the muscular texture, appear to belong in part to these varieties of proportion. Thus the phosphate of lime or gelatine, diminished by nutrition, give to the bones softness or brittleness.

It is in this fibrous and essential portion of the muscle, that particularly resides the faculty of crisping by the action of caloric, whether by plunging a muscle into boiling water, or exposing it to the fire; for this crisping is as evident in the muscle deprived of its colouring matter, its gelatine, its albumen, and even a portion of its extractive substance as in the ordinary muscle. There is in general a constant relation between the quantity of this fibrous substance contained in the muscles, and the quantity that the blood contains of it. In the strong, vigorous, sanguineous temperaments, as they are called, the muscles are thick and much more fibrous. In all the slow cachexiæ in which the blood is impoverished, the pulse small and feeble and in which muscular nutrition has had time to share but little of the fibrin of the blood, the muscles are small, weak, soft, &c. In general, the muscles and the blood are always in constant relation, whilst other systems often predominate and whilst this fluid seems to be in less quantity in the economy.

Exposed for a long time to ebullition, as in common boiled meat, the muscular texture, still united to the adjacent organs, and to its common parts, gives, 1st, an albuminous scum which appears to arise more from the lymph of the cells than from the muscle itself; 2d, many fatty drops coming also especially from the cellular texture, almost foreign consequently to the texture of the muscle, and which swim on its surface; 3d, gelatine formed especially by the aponeurotic intersections; 4th, an extractive substance which colours in part the water in which it is boiled, gives it a peculiar taste and remains in part adherent to the flesh to which it communicates a deep tinge wholly different from that of raw flesh, a tinge which arises also from the colouring matter of the muscle, and which moreover changes, when the liquor cools, into a less deep and even a whitish tinge; 5th, various salts which contribute much to the taste of the liquor, and the nature of which chemists have ascertained. These are the natural phenomena of the ebullition of the muscle.

The more extensive analysis of boiled flesh is not my province; but what ought not to escape us here, are the phenomena of which the fibre is the seat, whilst the preceding products are extracted, whether from it, or the surrounding textures. These phenomena can be referred to three periods. 1st. When the water is only tepid, and even a little above the temperature of the body, it leaves the muscular texture in the same state, or softens it a little. 2d. When it approaches ebullition and begins to be covered with an albuminous scum, the texture crisps, thickens and contracts and gives to the muscle a density much greater than what is natural to it, and augments considerably its resistance. I have observed that in this state the muscles bear much greater weights than in a natural state. They approximate, if we may so say, that remarkable density which characterizes them when they contract in the living body, and which so powerfully opposes their rupture. This condensation of the muscular texture, which is prompt and sudden, increases till the period of ebullition, when it is at its greatest height; it continues only for a certain time. 3d. Gradually it diminishes, the fibres soften, and are more easily torn than in their natural state. This softening, the reverse of the hardening that precedes, is produced slowly and by degrees. When arrived to a certain degree, the meat is rendered fit for the table. Observe that then the muscle has not returned to the state in which it was found before the hardening; among other phenomena which distinguish it, the following is an essential one; it has lost the power of crisping, of acquiring the horny hardness, from the action of the concentrated acids, from alkohol or from caloric. In general it becomes putrid more slowly. Its putrefaction does not give the same odour. We know how much its taste differs. The principles it has lost are undoubtedly one of the great causes of these differences.

When a muscle is exposed to an open fire, as in the roasting of meat, the albumen is condensed, the gelatine melts, the fibrin filled with juices softens, the extractive matter flows in part with the gelatine and the salts held in solution; it is this that forms the gravy, which is, as we know, very different from melted fat. The exterior of the meat remains more dense than the interior; it is coloured by the extractive substance. The interior loses in part its natural colour; its consistence, its taste and its composition even change entirely. The fibres, as in ebullition, lose the power of contracting and of crisping from the action of strong stimuli and especially that of fire.

No part in the animal economy is more easily altered by the digestive juices than the muscles. Almost all stomachs can bear boiled meat, whilst many reject other organs when cooked. Carnivorous animals seize upon the muscles of their prey in preference to the pectoral and gastric viscera. Muscular flesh is with most people the most common aliment, that with which they are never disgusted; it appears to be the most nourishing of all those, which are afforded by the different textures of animals; is it, as it has been said, because it contains the most azote? Whatever may be the reason, the general part which the muscular system takes in the digestion of all carnivorous animals, of man especially, is remarkable. Yet all the parts of this system do not appear to be equally agreeable to the taste of animals. It is, for example, a singular fact, that those bodies which are brought to our dissecting rooms, and which have been attacked by rats, are found almost always exclusively gnawed in the muscles of the face.