Part 32

The fibrous organs arranged as membranes are, 1st, the fibrous membranes, properly so called; 2d, the fibrous capsules; 3d, the tendinous sheaths; 4th, the aponeuroses.

1st. The fibrous membranes comprehend the periosteum, the dura-mater, the sclerotica, the albuginea, the peculiar membranes of the kidney, the spleen, &c. &c. They are in general destined to form the covering of certain organs, into the structure of which they enter.

2d. The fibrous capsules, very distinct, as we shall see, from the synovial surfaces, are a kind of cylindrical sacs, which are found around certain articulations, especially those of the humerus and the femur, whose connexions with the scapula and the ilium they strengthen, by embracing with their two extremities, both surfaces of the articulation.

3d. The fibrous sheaths are destined to confine the tendons in their passage upon the bones, where they are reflected, and generally wherever by muscular contraction they would be made to deviate and consequently transmit with difficulty to the bones the motion they receive from the muscles. They may be divided into two kinds; one receives and transmits the tendons of many muscles united, as is seen at the wrist, the instep, &c.; the other, like that of the fingers, is destined for a single tendon, or two only.

4th. The aponeuroses are a kind of fibrous nets more or less broad, entering always into the system of locomotion, and so arranged that they sometimes form coverings for different parts, and sometimes furnish the muscles with points of insertion. Hence the aponeuroses of covering and the aponeuroses of insertion; each of them is divided into species.

The aponeuroses of covering are placed sometimes around a muscle, to which they serve as a general sheath, as we see on the thigh, the fore-arm, &c.; sometimes upon certain muscles which they partially retain in their respective places, as that which goes from the posterior and superior serratus minor to the anterior and inferior, as the abdominal aponeurosis, as that situated anteriorly to the solæus, behind the deep muscles of the leg, &c.

The aponeuroses of insertion are sometimes with surfaces more or less broad, as in the attachments of the triceps femoris, the rectus, the biceps, &c.; sometimes with fibres separate from each other, and giving attachment by each of these fibres to a fleshy fibre, as at the superior insertion of the iliacus, of the anterior tibialis, &c.; sometimes finally in the form of an arch, and then at the same time that they give the muscles points of insertion, they allow vessels to pass under them, as in the diaphragm, the solæus, &c.

II. Of the Fibrous Organs in the form of Fasciæ.

The fibrous organs arranged in fasciæ are, 1st, the tendons; 2d, the ligaments.

1st. The tendons are found at the origin, insertion or middle of the muscles. They are either simple, in the form of elongated cords, as in the peronæus, the tibialis, and almost all the muscles, or compound, as in the rectus, the flexors, &c.

2d. The ligaments strengthen the osseous or cartilaginous articulations, around which they are found. They have regular fasciæ, as the lateral ligaments of the elbow, the knee, the jaw, &c.; or irregular fasciæ, as those of the pelvis.

III. Table of the Fibrous System.

We can in the following table present at a single view the classification of the fibrous organs that I have just pointed out.

┌ ┌Fibrous Membranes. │ │Fibrous Capsules. │ │ ┌Partial. │Of a membranous │Fibrous Sheaths. └General. │ form. │ ┌Partial. │ │ ┌For covering └General. FIBROUS │ │Aponeuroses │ ORGANS. │ │ │ ┌With a broad surface. │ └ └Of Insertion│In an arch. │ └With separate fibres. │ │ ┌Tendons ┌Simple. │In the form │ └Compound. │ of fasciæ. └Ligaments ┌With regular fasciæ. └ └With irregular fasciæ.

Though the numerous organs which enter into this classification, belong to very different apparatus, though they seem to be spread here and there in the economy, without holding together at all, and though all appear insulated, yet they are almost all continuous and connected; so that we may consider the fibrous system, like the vascular and cerebral nervous systems, that is to say, as having a common centre, from which all the different organs go that form its divisions.

This common centre of the fibrous system appears to me to be the periosteum, not that I pretend that like the heart or the brain, it sends out radiations upon the organs that go from it, but because anatomical inspection shows us that all the fibrous organs are intimately connected with it, and by its means communicate with each other; the following observations are a proof of this.

1st. Among the fibrous membranes, that of the corpus cavernosum intermixes with the periosteum below the ischium; the dura-mater is continued with it through the foramina at the base of the brain; by uniting itself by the lamina which accompanies the optic nerve to the sclerotica, it joins to it this membrane, and thus serves as an intermediate organ for them. 2d. All the fibrous capsules above and below the articulation intermix with the periosteum. 3d. Wherever fibrous sheaths exist their fibres intermix with those of the periosteum. 4th. All the aponeuroses either of covering or insertion have a similar intermixing. 5th. Wherever the tendons are expanded, they are also confounded with this membrane. 6th. At the two extremities of the ligaments it unites also its fibres to theirs. There are none scarcely except the albuginea, the perichondrium of the larynx, the membranes of the spleen and the kidney, that form an exception to this general rule.

The fibrous system should be considered then in a general manner, that is to say, as extending itself everywhere, belonging at the same time to many organic apparatus, distinct in each by its form, but continuous in the greatest number, having everywhere communications. This manner of describing it will appear still more natural, if we consider that the periosteum, the general boundary of the different portions of this system, is itself everywhere continuous, and at the place where the articulations divide it, the fibrous capsules and the ligaments serve, as we have said, to reunite it.

We understand from this use of the periosteum in relation to the fibrous system, what the advantage is of its situation upon the bones which offer it a solid support, and give the same also to the organs of which it is the boundary.

ARTICLE SECOND.

ORGANIZATION OF THE FIBROUS SYSTEM.

In the midst of the varieties of form that we have just examined, the general organization of the fibrous organs is always nearly the same. I shall now consider this organization; I shall treat elsewhere of the varieties it experiences in each part. It arises from the union of a peculiar texture and of the vascular, cellular systems, &c.

I. Of the Texture peculiar to the Organization of the Fibrous System.

Every fibrous organ has for a base a fibre of a peculiar nature; hard, but slightly elastic, insensible, scarcely at all contractile, sometimes in juxta-position and parallel to each other, as in the tendons and the ligaments, sometimes crossed in various directions, as in the membranes, the capsules, the fibrous sheaths, &c. but everywhere the same, everywhere of a white or greyish colour, and of a remarkable resistance.

This resistance of the fibrous texture enables all the organs that it composes to support the greatest efforts. Thus these organs are all destined to uses which require this faculty in them. The ligaments forcibly retain the articular surfaces in their proper relation. The aponeuroses confine the muscles and oppose their displacement. The tendons constantly exposed to the contraction of these organs, are at every instant placed between the strong power that they represent and the more or less considerable resistance situated at the extremity of the muscles, &c. Such is this resistance, that it is often greater than that of the bones themselves. We know that by muscular efforts alone, the patella, the olecranon process and the os calcis are sometimes broken; now this could not happen, if the extensor tendons, which corresponded to these different bones, were of a texture that could be more easily torn.

It is to this resistance that must be attributed the following phenomena: 1st. We experience the greatest difficulties in making luxations in the dead body, principally in the articulations called enarthrodial. 2d. In the living subject the external efforts are rarely sufficient to produce them; it is necessary that the powerful action of the muscles should be added. 3d. The punishment formerly employed, of drawing the limbs of criminals by attaching horses to them, was much more terrible, because the resistance of the ligaments made it continue longer; almost always the horses were unable to produce the separation of the extremities; it was necessary that a cutting instrument should assist their efforts. 4th. Weights suspended to a tendon do not break it unless they are enormous; thus the best strings to be employed in the arts would be these textures of the fibrous organs, if drying did not take from these organs their softness and flexibility, if moisture did not alter them, &c. 5th. We cannot without great efforts tear an aponeurosis, especially those of any thickness, as the fascia lata, the albuginea, the dura-mater, &c.

Yet this resistance is sometimes overcome in the living body, and we sometimes see the rupture of the tendons of the solæus, of the small plantaris, of the extensors of the thigh, &c. How does it happen, that the softer texture of the muscle never yields, whilst that of the tendon much more compact is broken? It is because in these cases the fleshy fibres are always in contraction; consequently far from being stretched, as the tendinous fibres are which are then found, if we may so say, passive, their different portions make an effort to approximate each other; and they do in fact approximate; this gives to the muscle a density and hardness equal, and in some cases even much greater, than those of their tendon, as we can ascertain by applying the hand upon a muscle in contraction. A proof that this kind of ruptures is owing to the cause I have mentioned, is this, that if in a dead body we suspend a weight to a muscle detached from the bone at one of its extremities, it will be the fleshy and not the tendinous portion that will break.

The fibrous texture has been considered by some anatomists, as being of a nature approaching that of the muscular texture, and even as being sometimes the continuation of it. Thus they have said that the tendon was formed only by an approximation of the fleshy fibres, which, without changing their nature, only lose their redness. Thus the aponeuroses of covering have been described as an effect of the pressure of the surrounding bodies upon the most external fleshy fibres. In order to see how little foundation there is for this opinion, it is sufficient to observe, 1st, that the dura-mater, the sclerotica, the periosteum, the ligaments, are evidently of the same nature as the tendons and the aponeuroses, and that yet they differ wholly from the muscular texture; 2d, that the chemical composition, the vital properties, the apparent texture, are entirely different in the tendinous and muscular fibre; 3d, that there is no relation between their functions. There is certainly less analogy between the muscle and the tendon which receives its insertion, than between that and the bone which furnishes an attachment to it, and whose cartilaginous portion approximates it in its nature. A muscle and its tendon form an organic apparatus and not a simple organ.