The fibro-cartilaginous system is composed of different organs which anatomists have sometimes placed among the cartilages, and sometimes among the ligaments, because they in fact partake of the nature of both. I make a system of them between the two preceding ones, a knowledge of which will facilitate the understanding of this.

ARTICLE FIRST.
OF THE FORMS OF THE FIBRO-CARTILAGINOUS SYSTEM.

We may divide the fibro-cartilaginous organs into three classes.

The first comprehends those which are found in the ears, the alÆ of the nose, the trachea, the eye-lids, &c. They are very delicate, like membranes, sometimes arranged in an uniform manner, sometimes bent in various directions. As neither their position nor functions have any thing in common, we cannot give them a denomination derived from their forms. We may designate these substances by the name of membranous fibro-cartilages. Besides it is not only in its form, but also in its nature, that this class differs from the others, as we shall see.

In the second class are ranked the inter-articular substances, which occupy the interstices of the moveable articulations, whether they are in part loose in the cavity, like those of the knee, of the lower jaw, &c. and go in different directions according to the motions, or whether, like that of the body of the vertebrÆ, they are fixed in a solid, though moveable manner, on the osseous surfaces. These organs are in general thicker than the preceding, very various in their form, representing commonly a kind of laminÆ, sometimes perforated through the middle in the articular cavities, arranged in very thick fasciÆ, and formed like the body of the vertebrÆ in the vertebral column. We may designate them under the name of articular fibro-cartilages.

I refer to the third class certain portions of the periosteum in which the nature of this membrane is entirely changed, becomes penetrated with gelatine and exhibits an aspect at first analogous to that of the cartilages, but in which it is easy however to distinguish the fibrous texture. These portions are found in the tendinous sheaths, in which they facilitate the sliding of the tendons, and defend the bones from their impression. They may be called the fibro-cartilages of the tendinous sheaths.

These three classes of fibro-cartilages, though very analogous, have not exactly the same structure, the same vital properties, nor the same life; so that the system they form is not as homogeneous in its different divisions, as the osseous, animal muscular systems, &c.

ARTICLE SECOND.
ORGANIZATION OF THE FIBRO-CARTILAGINOUS SYSTEM.

I. Texture peculiar to the Organization of the Fibro-Cartilaginous System.

The texture peculiar to the organization of the fibro-cartilaginous system is composed, as its name indicates, of a fibrous substance, more than of a true cartilage.

The fibrous substance is as the base of the organ. We distinguish this base very plainly in the fibro-cartilages of the tendinous grooves and of the articulations, in those especially of the body of the vertebrÆ; it is much less apparent in the membranous fibro-cartilages. Its fibres are sometimes interlaced, sometimes parallel. In general its nature is exactly the same as in the fibrous system, hard, resisting, dense and compact, hence the very great force which the organs of this system have; hence, 1st, the solidity with which the vertebrÆ are kept together; 2d, the difficulty of rupturing, or tearing the fibro-cartilages of the knee, the jaw, the clavicle, &c.; 3d, the resistance which that of the radius makes to the inferior luxations of this bone, luxations which in the forced pronations of this bone have great tendency to take place, and which cannot without the rupture of this fibro-cartilage. I have seen an example of a similar displacement not reduced; the fibro-cartilage was entirely gone; 4th, by bending the true cartilages they break nearly like a radish; these organs on the contrary bend in all directions, and resist the agents that stretch them; 5th, we see men imprudently raise children by their ears, the fibro-cartilages of which easily support the weight of the whole body. I am persuaded that those of the nose would do the same. 6th. We know that in the aneurisms of the pectoral or the abdominal aorta, the bodies even of the vertebrÆ are much more quickly worn, and consequently resist less than the substances which unite them.

The cartilaginous portion appears to be interposed between the fibres, the interstices of which it fills. It is very evident especially in the articular fibro-cartilages and in those of the grooves; it is from it that they borrow the white colour that characterizes them, the inorganic appearance that a section of them exhibits in many places, and the elasticity which they have. Subjected to ebullition, the articular fibro-cartilages, like those of the tendinous grooves, become yellow, transparent, melt into gelatine, though with much more difficulty than the true cartilages.

As to the membranous fibro-cartilages of the ear, the nose, the trachea, the epiglottis and the eye-lids, their composition appears to be very different. The action of boiling water does not reduce them to a gelatinous state, at least in an evident manner; they remain white, soften a little, appear wholly different from a fibrous organ or the other fibro-cartilaginous organs boiled, which dissolve after becoming yellow and semi-transparent. The inspection of the ears of animals that are brought on our tables clearly proves this; I have frequently confirmed it in my experiments. I know but few of the textures in the economy that resemble this. When it has been boiled a little while, the kind of periosteum which surrounds it is detached from it; it breaks itself and cracks in many places; the rings of the trachea especially exhibit an example of this last phenomenon.

Exposed for some days to maceration, this texture, from being white, becomes of a very evident red. This colour is deeper than that which the cartilages of ossification acquire in water; does it arise from the same causes? I know not.

When the intervertebral fibro-cartilages are macerated, their fibrous laminÆ take also their reddish tinge, which I have not seen in the other articular fibro-cartilages, especially in those of the knee.

Drying makes the membranous fibro-cartilages hard and brittle; they do not take then the yellow colour of the dried tendons and aponeuroses; they have a peculiar appearance.

Subjected to this experiment, the intervertebral substances acquire a remarkable transparency, different also from that of the fibrous system, without the yellowish tinge. In the first days of their maceration, these substances, when they have been entirely detached from the vertebrÆ, swell, rise up and form a kind of hollow cone, the summit of which is made by the middle which especially swells, and the base by the circumference which remains nearly in the natural state.

Most of the fibro-cartilages want in general the perichondrium; this is evident in those of the tendinous grooves in which the bone on one side and the synovial membrane on the other cover the organ, in those of the articulations which this membrane surrounds on both sides, and in those of the vertebrÆ to which only the anterior and posterior vertebral ligaments correspond. As to the membranous fibro-cartilages, there is upon them a very distinct fibrous texture; it is thick, closely united to the peculiar texture of the organ, easily seen by maceration, which whitens it in an evident manner, and which thus makes it wholly different from the fibro-cartilaginous texture which is in the middle. By cutting a fibro-cartilage of the ear, the nose, that of the epiglottis, &c. after they have remained in water, this fact is made very clear, especially during the period in which they have the redness that I have pointed out.

The fibro-cartilaginous system appears to have nearly the same relations with the digestive juices, as the fibrous and cartilaginous systems, of the nature of which it partakes; it is altered with difficulty by those juices in a crude state. Boiling, by softening, makes it yield more to their action; it becomes then more digestible. In general, it gives an aliment less proper for nutrition, than that furnished by many other systems.

II. Parts common to the Organization of the Fibro-cartilaginous System.

The common organs of the fibro-cartilages are not very conspicuous; the cellular texture is in small quantity, and so compact as hardly to be distinguished; maceration however renders it apparent.

But little blood enters their vascular system in the ordinary state; I convinced myself of this by dissecting an animal killed for the purpose by asphyxia, a disease in which the blood accumulating in the capillaries intermediate to the arteries and the veins, towards the head especially, renders these capillaries very evident; but in inflammation, which is however rare in the fibro-cartilages, they are very much injected. We can trace no nerves in them.

ARTICLE THIRD.
PROPERTIES OF THE FIBRO-CARTILAGINOUS SYSTEM.

I. Physical Properties.

Elasticity belongs essentially to this system. This property is very evident, 1st, in the fibro-cartilages of the ears, when we bend them; 2d, in those of the nose, when twisted in various directions; 3d, in those of the trachea, when we compress them, or after having cut them longitudinally, we separate the edges of the division, as is done in tracheotomy, when the object is the extraction of a foreign body. It performs an important use in the kind of vibration which is made in the first in the perception of sounds, in the second in the production of the voice; 4th, it is in virtue of their elasticity, that the articular fibro-cartilages serve as a kind of cushions which favour, by contracting and expanding, the motion of the osseous surfaces to which they correspond; 5th, that those of the vertebrÆ in particular, flattened during the day, re-act during rest, and thus make the stature in the morning something more than it is in the evening; 6th, finally in the sliding of the tendons upon their fibro-cartilages, the elasticity of these last favours the motion in an evident manner.

This elasticity of the fibro-cartilages is united to a remarkable suppleness; they bend in all directions without breaking. By the first property they resemble especially the cartilaginous system; by the second they approximate the fibrous. It is not astonishing that being intermediate to these two systems in their texture, they should be so also in their properties.

II. Properties of Texture.

Extensibility is very often brought into action in the fibro-cartilaginous system. I have seen a polypus that had so dilated the anterior openings and consequently the fibro-cartilages of the nostrils, that their diameter was at least treble. The external and cartilaginous extremity of the meatus auditorius often exhibits from the same cause, an analogous distension. In the various twistings of the vertebral column, the portion of the fibro-cartilages corresponding to the convexity of the curvatures, is evidently elongated, whilst the opposite portion is contracted. This extensibility is moreover subjected in many cases to the same law as in the fibrous system, that is to say that it cannot be put into action but in a gradual and insensible manner.

The contractility of texture is observed when, in the cases of which I have spoken, the cause of distension disappears. Thus after the extraction of the polypus mentioned, the nostril gradually resumes its natural diameter. I have removed in a dog a tendon from its groove, by cutting it at one extremity, and drawing it by the other, so as to leave untouched and empty the sheath that contained it; this sheath and the fibro-cartilage have gradually contracted and the cavity has disappeared. In the carcinoma of the eye, in which the eye-lids were not removed, the tarsi which become much elongated with these moveable veils, gradually contract and resume their dimensions, after the extirpation of the tumour which distended them. It is necessary however to distinguish these phenomena from those which are the product of elasticity; these last are prompt and sudden; the fibro-cartilage of the ear, powerfully stretched, yields a little, and immediately goes back again; the others, on the contrary, are characterized most often by a remarkable slowness.

III. Vital Properties.

All the vital properties appear to be but little developed in the fibro-cartilages; there is no animal sensibility or contractility in the natural state; the first appears however in inflammation. Organic sensibility and insensible contractility are only found in the degree necessary for nutrition. There is no sensible organic contractility.

This obscurity in the vital properties, gives to all the phenomena of the life of the organs of which we are treating, a remarkable slowness. I have observed that in making in the ears of a dog a longitudinal section, and afterwards uniting the wound by a suture, the skin, at the end of a few days, is entirely closed; but it is only at the expiration of a much longer time, that the union of the cartilage takes place below, as we can see by examining the parts after the union of the integuments. I presume that the same thing happened in the operation of tracheotomy formerly employed, in which the soft parts forming at first the cicatrix, keep in contact the cartilaginous semi-rings, which finally unite together.

It is also to this obscurity of the vital properties of the fibro-cartilages, to their want of energy, that must undoubtedly be referred the rareness of diseases of these organs. I know but few of the organic systems in the economy, which are more rarely affected than that of the fibro-cartilages of the nose, of the ears, the trachea, &c. Gangrene attacks them with difficulty; they are scarcely altered by it, whilst the soft parts which surround them are all already black. We know but little of the kind of fluid they form in their suppuration. The formation of pus appears to be even very rare in them, owing to their want of vital activity.

As these organs are hardly ever diseased, we can with difficulty know their sympathies; I am unable to cite an example of them.

ARTICLE FOURTH.
DEVELOPMENT OF THE FIBRO-CARTILAGINOUS SYSTEM.

I. State of this System in the first age.

In the first periods of existence, the articular fibro-cartilages are much developed, which appears to be the effect of the size of the articulations at this period. In fact, as the extremities of the bones are larger in proportion, whilst they are cartilaginous, than when they are in the osseous state, the articulations are also proportionally larger, and the organs they contain more developed.

The fibro-cartilages of the grooves, which are found almost all, as we know, situated at the extremities of the long bones, are not, in the first age distinct from the cartilages of ossification, which then form these extremities. Confounded with them, they exhibit no line of demarcation when we cut the lines at that place. This state continues until complete ossification; then the fibro-cartilages of the grooves remain insulated like the cartilages of the osseous extremities.

The interposed gelatinous portion appears to predominate, in childhood, over the fibrous portion in the articular fibro-cartilages and in those of the grooves. It is remarkable in the intervertebral substances, in which this kind of mucilage which occupies the centre, is as to quantity in the inverse ratio of the age, and in which the fibres are also more developed. On the pubis, the whole is almost homogeneous in the foetus; the transverse fibres do not become very apparent till a more advanced age. The articulations of the knee, the jaw, &c. have in their fibro-cartilages, the same arrangement. Ebullition extracts from them then a much greater quantity of gelatine; they have more the smooth appearance of the cartilages.

The membranous fibro-cartilages are in general developed early, those of the ear, the eyes and the nose especially. We see them very evident in the foetus. I have observed in two acephalous infants, that, like all the other parts of the face, they were of a remarkable size, and much greater than that of the ordinary state. Besides, the whole fibro-cartilaginous system is, in the foetus, extremely soft, supple and unresisting.

II. State of the Fibro-Cartilaginous System in the after ages.

This system becomes stronger as we advance in age; in old age, it becomes hard and yields with difficulty from the peculiar nature of its nutritive substances. It is to this circumstance that must be attributed, 1st, the stiffness and inflexibility of the vertebral column, whose fibro-cartilages keep all the pieces in a kind of immobility; 2d, a part of the difficulties which an old person experiences in hearing sounds, the concha not being able to vibrate and reflect them as well as before; 3d, the less susceptibility of his nostrils to dilate, the fibro-cartilages yielding less to the muscular effort, which is besides also less; 4th, the difficulties of the sliding of the tendons, their grooves being much less supple.

The fibro-cartilages have in general much less tendency to ossify in old age, than the cartilages properly so called. I never saw this phenomenon in the membranous ones; perhaps it arises from their peculiar texture, and even the difference of the principles which go to their composition, and from the small quantity of gelatine that enters into them. Among the articular, there are scarcely any but those of the vertebrÆ, which are sometimes entered by the phosphate of lime; this is however rare. Those of the grooves are like the cartilages of the moveable articulations, they constantly keep their nature; only in extreme old age, their thickness appears to diminish a little by the ossification of their laminÆ which correspond to the bone, which besides is not very evident.