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.