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 fœtus; 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 fœtus. 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 fœtus, 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.
MUSCULAR SYSTEM OF ANIMAL LIFE.
The general muscular system very evidently forms two great divisions, differing essentially from each other, by the vital forces that animate them, by their external forms, by their mode of organization, and especially by the parts they perform, the one in animal life, and the other in organic. We shall not then consider them together. Let us begin by the examination of the muscles of animal life; these are spread out in great number in the human body. No system as a whole, is of more considerable size; no one occupies more space in the economy. Besides the numerous regions that the muscles fill, they are generally spread out under the skin, and partake, as it were, of the functions of this organ, protect like it the subjacent parts, like it bear with impunity the action of external bodies, and can even be divided in a more or less considerable extent, without the general functions of life suffering from it; which renders them very fit to defend the deep-seated organs, whose lesion would be very injurious.