Part 27

Observe in regard to the use of the muscles in digestion, that it is the portion of the fibrous system which adheres to them, and forms, as it were, a part of them, I refer to the tendons, which is the most easily altered by maceration, by ebullition and by the digestive juices. Observe also that the great mass which the muscles form in the body of all animals, of which they are more than one third, presents to the carnivorous species ample materials for their nutrition; thus nature, by multiplying these organs for the wants of the individual which they move, seems to multiply them also for those of the individuals which he is one day to nourish. In forming them in each species, it labours for other species as well as for this. Who knows if this general design, which observation finds in the series of all animals, be not the cause of this remarkable predominance which the muscles have over the other systems? Who knows, if nature would not have diminished the powers of the animal mechanism which are so numerous and so complicated in comparison with those of artificial machines, who knows if she would not have simplified the means and given the same results, if the motions of the animals had been the only object of the formation of the muscles?

The sex has great influence on the quality of the flesh of animals. I do not believe that any thing precise is known as to the nature of the influence which the genital parts exert upon it; but the following are remarkable facts upon this subject. The muscles of males are stronger and better nourished, have more taste, resist boiling for a longer time, are firmer, &c. Boiling water on the contrary alters quicker the texture of females; it is more tender and gives to the liquor a less strong taste. In the season of sexual intercourse, the muscular system of the first has a peculiar odour, which often renders it disagreeable even to the taste. It is an observation that is easily made in quadrupeds, birds and fishes that are brought to our tables. Without having as strong an odour, the flesh of the second becomes at this period soft, flaccid and but little savoury.

II. _Parts common to the Organization of the Muscular System of Animal Life._

_Cellular Texture._

The cellular texture is very abundant in the muscular system; I know of no system that has a greater proportion of it. This texture forms a very evident covering around each muscle. This covering is most commonly loose, filled with fat, easily distended with air in emphysema and serum in anasarca. At other times it is more dense, compact and really arranged like a membrane. Such, for example, is the case with that which covers the great oblique muscle of the abdomen, and the dissection of which on this account, students at first find very difficult. The other abdominal muscles, the trapezius, the serratus major and the great dorsal exhibit also this arrangement. We might say that in this way nature compensated for the aponeuroses, which are wanting on the broad muscles of the trunk. Besides, this covering has only a membranous appearance; it has nothing of its organization, it disappears in the infiltration in which all the true membranes remain.

Besides this general covering of the muscle, each fasciculus has a less covering, each fibre a still less one, and each smaller one a real though almost insensible sheath. We can then represent the cellular texture of the muscles as forming a series of coverings successively decreasing. These coverings favour the motion of the fibres which they separate, either by the serum of the cells, or by the fat they contain, both fluids, by lubricating, allow them to slip more easily upon each other. Frequently between these fibres, the cellular texture appears to form a kind of cross pieces which go at right angles. We see this arrangement especially in the proper extensor of the great toe, and in the common extensor, the fleshy fasciculi of which are broad and delicate when distended. In most of the thick muscles nothing similar is observed.

The quantity of intermuscular cellular texture is remarkably variable. In general, in all the broad muscles and in all the large, long muscles, it is very abundant. It is less in proportion between the fibres of those of the vertebral canals. Back of the neck, the splenii, complexi, &c. have less of it than many others, especially in the spaces that separate them.

Sometimes very considerable cellular elongations are found in the middle of the muscles, and seem to divide them into two; such is that which separates the clavicular portion of the great pectoral; this has even sometimes embarrassed anatomists as to the division of these organs.

The cellular texture in general fixes the muscles in their position; the art of dissection proves it. The effusions of pus which often perform the office of the scalpel, render also very evident this use, which does not prevent the motion in all directions, that the great extensibility of the cellular texture allows. The cellular texture not only fixes the muscles to each other, but it also attaches each of their fibres to neighbouring ones; it flattens them when they contract, and elongates them when they are distended; if they are deprived of it their motions become irregular and uncertain. I have many times separated with a scalpel a muscle laid bare in a living animal, into many small fasciculi; in afterwards making this muscle contract by the irritation of the medulla, by means of a stilet introduced into its canal, I have observed in an evident manner this irregularity of motion. Cut longitudinally a muscle of an extremity from its superior tendon to its inferior, so as to divide it into two or three entirely distinct portions, irritate afterwards one of these portions, the other or the two others will remain almost always at rest, whilst a single irritated fibre in a sound muscle, puts in motion the whole of that muscle. The section of the vessels and the nerves has no doubt a little influence upon this phenomenon; but that of the cellular texture certainly contributes to it also.

In dropsical subjects, the serum of the intermuscular texture is often reddish; this phenomenon is owing to the action of this serum after death upon the colouring substance. I believe that this can take place during life only with great difficulty. The fat sometimes abounds in this texture, to such a degree that the fleshy fibres disappear and the fat only is visible; but oftentimes also the yellow appearance of the muscular fibres, which is produced by the absence of the colouring substance, is taken for this fatty state of the muscles. I have seen the first state but rarely; the second is extremely frequent; we are sometimes deceived at first view. But ebullition and combustion easily prove, that the fat is wholly foreign to this want of colour of the muscles examined in this state.

_Blood Vessels._

The arteries of the muscles are very apparent; they come from the neighbouring trunks, penetrate the whole circumference of the organ, more however towards its middle, than towards its extremities. They run at first between the principal fasiculi, then divide and their divisions go between the secondary fasciculi, subdivide and wind between the fibres, and finally become capillaries and accompany the small fibres, in which they deposit by the exhalant system the nutritive matter. There are but few organs, which have, in proportion to their size, more blood than the muscles.

The blood is essentially necessary to support their excitability, as we shall see; it is that which colours the muscular texture, but not, as it at first seems, by circulating in its texture. The circulating or free portion contributes but little to it. It is the portion combined with the muscular texture, that which contributes to its nutrition, that gives it its colour; the following are proofs of it: 1st. The fibres of the intestines are as much or more penetrated with the circulating blood, than those of the muscles of animal life, and yet their texture is evidently whitish, where these vessels are not found. 2d. Many animals with red and cold blood, frogs in particular, have muscles almost white, and yet many red vessels run through this white texture. 3d. I have observed that in animals destroyed by asphyxia, the colouring substance does not change colour, no doubt because it is slowly combined with the muscle by nutrition; that on the contrary, if we cut a muscle of these animals in the last moments of life, whilst the venous blood still circulates in the arterial system, this blood flows out by black jets from the muscular arteries, the muscular texture itself remaining red. This curious experiment, which I have noticed in another work, is made by producing asphyxia in an animal by compressing the trachea, or by intercepting the air in any other way in this tube, whilst we examine the system of the muscles. When a muscle has been exposed for some time to the contact of the air, to that of oxygen especially, its red colour becomes evidently more brilliant.

The muscular vessels permit under certain circumstances the escape of the blood they contain; hence different kinds of remarkable hemorrhages, especially in scorbutic patients, sometimes in putrid fevers, rarely or never in those diseases that are characterized by an increase of vitality. Infiltrated with blood in preternatural hemorrhages, particularly in false aneurisms, the muscles lose in part their motion; this happens also in contusions, in which similar infiltrations are observed.

The veins everywhere follow the arteries in the muscles; they have the same distributions, and receive from the contractions of these organs an essential assistance to their action. The throw of blood is more powerful when the patient we have bled contracts his muscles, than when he relaxes them; the fluid is as it were expressed, as from a wet sponge which is squeezed. The arterial circulation does not exhibit this phenomenon. I have observed that if we open the artery of the foot of an animal, and by the irritation of the nerves, make the muscles of the leg and thigh, through which this artery passes before reaching the foot, contract powerfully, the throw of blood is not stronger than during the relaxation.

I have many times injected the veins of the muscles of animal life with ease, from the trunks towards the branches, which makes me believe, notwithstanding what Haller has said, that in these organs, as in the heart, the valves are less numerous than in many others. No doubt the assistance the veins derive from their surrounding organs supplies the place of these folds, or rather renders them useless, the weight of the column of blood not making a great effort against the venous parietes. The varices of the muscular veins are, as we know, extremely rare. These veins are of two orders; one accompanies the arteries and follows the same course, the others are spread superficially on the surface of the organ, without having corresponding arteries.

There are absorbents and exhalants in the muscles; but we can with difficulty trace the first, and the second cannot be perceived.

_Nerves._

Almost all the nerves of the muscles of animal life come from the brain; the ganglions furnish a few of them; when this happens, as in the neck, the pelvis, &c. besides the filaments coming from these nervous centres, there are always filaments of cerebral nerves; without this, these muscles would be involuntary. Few organs receive more nerves in proportion to their size than the muscles. In general the extensors appear to have rather fewer than the flexors; but the difference is trifling. It is true that all the great nervous trunks are in the direction of flexion, that in that of extension there are only branches, as we see in the posterior part of the arm, of the fore-arm, the vertebral column, &c. It is true also that this remark is likewise applicable to the existence of the vessels, which are larger and more numerous in the first than in the second direction; but this greater number of vessels and nerves arises from this, that there are many more flexors than extensors, that the first are stronger and have more numerous fibres; so that each of these fibres hardly receives more nervous or vascular filaments in one kind of muscles than in the other. I think that there is but little foundation for what has been said upon the difference of the strength of the fibres of the flexors and of the extensors, upon the predominance of the first, &c. If these are superior, it is either because they are more numerous, as in the foot, the hand, &c. or more advantageously arranged, as in the trunk on which the abdominal muscles act very far from the point of attachment to bend the spine, whilst to extend it, the dorsal muscles exert their action immediately at the side of this point of attachment, as also in the neck, where the muscles that draw down the lower jaw and head when this bone is fixed, are much further from the occipital condyles, than the muscles which produce extension. Whatever may be the cause of the superiority of the flexors, the fact cannot be doubted. 1st. In hysterical convulsions, in those of infants, in all the spasmodic motions in which the will has no part, the contractions take place much more in the direction of flexion than in that of extension. 2d. In old people the flexors finally become superior to the extensors; for example, the fingers and toes are almost uniformly bent. 3d. In all the motions, the power is always on the side of flexion.

The nerves enter the muscles of the extremities at a very acute angle, because the nervous trunks are in the natural direction of these organs. In the trunk, on the contrary, the nerves going from the spine, the cervical especially, enter their muscles at almost a right angle or one less evidently acute; this circumstance is of no importance. Each branch in the fleshy fibres, is at first divided and then sub-divided in their interstices, and afterwards lost in their texture. Does each fibre receive a small nervous filament? We should be led to believe so from this observation, that the principal branch being irritated, all the fibres are put into action, no one remains inert. But on the other hand, if we irritate one of them, all move also, which is certainly a sympathetic phenomenon or one arising from the communication of the cells.

Are the nerves deprived of their cellular coverings, and do they become pulpy when they enter the muscles? Dissection has shewn me nothing like it.

ARTICLE THIRD.

PROPERTIES OF THE MUSCULAR SYSTEM OF ANIMAL LIFE.

There are but few systems in the economy in which the vital properties and those of texture are found in so great and evident a degree as in this. It is from the muscles that examples must be selected to give a precise and accurate idea of these properties. The physical properties on the contrary are slightly marked in them; a remarkable softness characterizes them; there is no elastic power in their texture; there is but very little resistance from this texture after death; it is from vitality that it derives the power that characterizes it in its functions.

I. _Properties of Texture. Extensibility._

Extensibility is manifested in the animal muscular system under many circumstances. The different motions of our parts render this property evident. Such is in fact the arrangement of the muscular system, that one of its portions cannot contract, without the distension of another. The thigh being strongly bent, the semi-membranosus, the semi-tendinosus and the biceps are elongated. The arm being carried out, the great pectoral is extended, being raised, the great dorsal and the teres major are stretched. All the great flexions bring into action this property in the extensors; all the extensions render it evident in the flexors. A muscle which is stretched by its antagonist is in a state purely passive; it is as it were for a moment abandoned by its contractility, or rather it possesses it, without its being brought into action; it is made to obey the motion that is communicated to it. Observe that in these cases, the distension is confined to the fleshy portion, and the tendon has no connexion with it; it remains the same, whatever may be the distance, of the points of attachment, for these points are nearer or more remote in the different extensions to which the muscles are exposed; the longest muscles yield the easiest. The sartorius, the posterior muscles of the thigh, &c. exhibit this phenomenon in an evident manner; as their position is accommodated to it. In general all the muscles remarkable for their length are superficial, and go most commonly to two articulations, sometimes even to three or four, as in the limbs. Now the number of these articulations renders the space comprised between the two points of attachment susceptible of very great variations, which the great extensibility of these muscles allows. It may be understood from what has been said above, that it is to the length of the fleshy fibres and to the whole length of the muscle, that its degree of extensibility is to be referred. Those in which many aponeuroses are intermixed, and which derive in part from these membranes or from tendons their length, possess less of this property. Hence why, in the same motions, muscles of the same total length become more or less short, more or less elongated in their fleshy portion. Observe however that when on the one hand the tendinous portion predominates much, and on the other that it is very delicate, it yields a little, as we see in the small plantar and palmar muscles.

If from the natural state we pass to the morbid, we see the muscular extensibility manifested in a much more evident degree. In the face, the air accumulated in the mouth, swells it by elongating the buccinators; the various tumours of this cavity, as the fungous and sarcomatous ones, often distend the small facial muscles in a manner which would astonish us, if we considered the naturally small extent of these muscles which are trebled and even quadrupled. The muscles of the eye-lids and the eye in the large carcinomas of that organ, those of the anterior part of the neck in the great swellings of the thyroid gland, the great pectoral in large aneurisms or in other tumours of the axilla, the abdominal muscles in pregnancy, in dropsy, in the various tumours of the abdomen, &c. the broad and superficial muscles of the back from wens that are under them, present us these phenomena of distension in a remarkable manner. The muscles of the extremities are less subject to them, because on the one hand fewer causes develop tumours beneath them, and because on the other the aponeuroses do not yield so easily to these phenomena.

_Contractility of Texture._

The contractility of texture is carried to the highest point in the muscles. These organs have a continual tendency to contraction, especially when by being elongated, they have surpassed their natural size. This tendency is independent of the action of the nerves, and of the irritable property of the muscular texture. It is influenced by life, but it is not entirely dependent on it; it depends essentially on the structure of the muscles. The remarkable phenomenon of the antagonist muscles results from it. The following is this phenomenon.

Each moveable point of the animal frame is always between two opposite muscular forces, between those of flexion and extension, of elevation and depression, of adduction and abduction, of rotation without and rotation within, &c. This opposition is a condition essential to the motions; for in order to perform one of them, it is necessary that the moveable point should be in the opposite motion; in order to bend, it is necessary that it should be first extended, and reciprocally. The two opposite positions which a moveable part takes, are for it alternately the point of departure and the point of arrival; the two extremes of these positions are the two limits between which it can move. Now between these limits there is a middle point; it is the point of rest of the moveable part; when it is found there, the muscles are in their natural state; when it passes it, some are extended, others are contracted, and such is their arrangement, that the contraction and extension which take place in an opposite direction, are exactly in direct ratio. Hence, in the reciprocal influence that the muscles exert upon each other, they are alternately active and passive, power and resistance, organs moved and organs which move. The effect of every muscle which contracts is not then only to act upon the bone in which it is inserted, but also upon the opposite muscle. Between two muscles thus opposed, there is often no solid intermediate organs, as in the lips, the linea alba, &c. The muscle of one side acts then directly upon that which corresponds to it, in order to distend it. Now this action of the muscles upon each other is precisely the phenomenon of the antagonists; two muscles are such when one cannot contract without elongating the other and vice versa. Let us examine in this phenomenon the part of the contractility of texture; it is necessary to distinguish its influence from that of the vital forces, which has not been heretofore sufficiently done.

A muscle once placed in the middle position, can only be removed from it by the influence of the vital forces, by the animal or sensible organic contractility, because in this position the contractility of texture of its antagonist is equal to its own, and there is consequently required a force added to this to overcome that which is opposed to it. But if the muscle is found in one of the two extreme positions, for example in adduction, abduction, flexion, extension, &c. then there will be an inequality of action in the antagonists, as it respects the contractility of texture; the one most stretched, will make in order to contract itself, an effort much greater than that which is already contracted. To maintain the equilibrium, it is necessary then that the vital forces continue to influence the contracted muscles. Thus every extreme position of the limbs and of any moveable part, cannot in an ordinary state be supported except by the influence of the vital forces. When these forces cease to be in action, immediately the contractility of texture of the elongated muscle, which had a tendency to exert itself, but was prevented, exerts itself, becomes efficacious, and draws back the moveable part to the middle position, a position in which the equilibrium is restored. Hence why in all the cases in which the cerebral influence has no power over the muscles, in which they are not irritated by stimulants, the limbs are uniformly found in a medium position between extension and flexion, abduction and adduction, &c. This is the case in sleep, in the fœtus, &c. I have shewn elsewhere how the osseous arrangement of each articulation is adapted to this phenomenon, how every kind of relation between the articular surfaces, except that of this medium position, exhibits a forced state in which some ligaments are necessarily more stretched than others, and in which the osseous surfaces are never in so general contact as in this position. In certain fevers which have so deleterious an influence upon the muscular life and texture, the horizontal prostration and extension of the extremities do not arise from an increase of the action of the extensors, but from the want of energy of the flexors, which have not power to overcome the weight of the limb; thus observe that every analogous attitude always coincides with the signs of general weakness; this is the attitude of putrid fevers, &c.

The section of a living muscle presents us with two phenomena which are evidently the product of the contractility of texture.