Part 31

ARTICLE FOURTH.

DEVELOPMENT OF THE CARTILAGINOUS SYSTEM.

The osseous and cartilaginous systems are confounded in the embryo; as the first is developed, the second contracts; the latter very evidently has gelatine for its principal base; I shall not return to the proofs that have demonstrated it in the osseous system.

I have shown, in speaking of that system, how the cellular and vascular parenchyma, existing at first alone and constituting the mucous state, is penetrated afterwards with this base, which forms the cartilage. The primitive mode of the formation of these organs is then already known. Let us see how its development continues.

I. State of the Cartilaginous System in the first age.

As ossification advances in the bones and gelatine is consequently carried to them in less quantity, it seems that it goes more abundantly to the articular surfaces; for the cartilages that are met with, then lose their primitive softness, and have a consistence that is constantly increasing. Yet much more gelatine leaves the bones, than is carried to the cartilages; so that we may say that this substance is continually diminishing, in the organs, in proportion as we advance in age. We know that it is the parts of young animals particularly, that are selected to make glue, jelly, &c. The articular cartilages at this period exhibit a phenomenon that I have frequently noticed in my experiments; when we macerate them in water for two or three days, they take a very evident red colour. This colour does not penetrate deeply; but if we cut the cartilage in many places so as to bring the fluid in contact with its interior, the whole of it becomes red. The cartilages of ossification exhibit the same phenomenon, which becomes less conspicuous as we advance in age; so that in adults generally, the cartilages do not lose their white colour by maceration. In some however they take a reddish tinge which is infinitely less bright than in the fœtus. Whence arises this phenomenon? Does the water give to the cartilage the cause of its colour, or does it take from it by solution certain substances which prevented this colour from being developed? Whatever may be the cause, none of the organs of articulation redden in this way; all on the contrary, the synovial, the ligaments, &c. become whiter.

There is usually no sensible demarcation between the cartilage that is to become bone, and that which is to remain as it is; sometimes however on the one hand we observe it a more dull colour at the extremity of the bones, whilst on the other, we never discover the reddish streaks, which are so frequently seen irregularly scattered on the cartilages of ossification.

As long as ossification continues, there is between the cartilage and the osseous portion already formed, a very evident vascular layer, and it is extremely easy to separate these two portions, which adhere but slightly to each other. We observe also on the surface of each when they are separated, several inequalities, projections and depressions reciprocally adapted to each other. It is the want of adhesion of the cartilaginous and osseous portions, before complete ossification, which has no doubt given rise to all that has been written upon the separation of the epiphyses, a separation which the observations of modern surgeons have rarely confirmed.

As the calcareous substance arrives at the extremities of the bone, the vessels gradually disappear, and the adhesions increase. Finally, the ossification being finished, there is no longer, on the one hand, an evident vascular net-work between the cartilage and the bone; and on the other, their union is such, that all rupture between them is almost impossible. These two characters especially distinguish the relation of the cartilage of ossification with the bone, from that of the real cartilage with the same bone. I have observed also that almost always above its union with the osseous portion, the cartilage of ossification has less whiteness, a deeper tinge, which extends the distance of two or three lines, and whose difference is often very considerable; this is the forerunner of the access of the blood. This arrangement does not exist in the cartilage of the bones of the adult.

We attribute commonly to the articular motions, the want of ossification of the cartilages of the moveable articulations; but I believe that it depends wholly upon the laws of osseous nutrition. Nature limits there the exhalation of the phosphate of lime, as it limits at the origin of a tendon the exhalation of the fibrin of the muscle which corresponds to it; it is because the mode of organic sensibility changes and the vessels of the cartilages are no longer in relation with the red part of the blood nor with the calcareous substance. In fact, by supposing the preceding hypothesis true, why do the cartilages of the immoveable articulations exist? Why should the motion which elsewhere favours exhalations and secretions, prevent here the first of these? Why do preternatural ossifications take place in the most moveable parts, of which the arteries furnish us an example? Why, in many anchyloses in which the articular surfaces unite, and in which the motion is destroyed, do not the cartilages disappear?

The cartilages of the cavities have a mode of origin, development and nutrition, perfectly analogous to that of the articular cartilages. I would observe that their texture differs, as well as the texture of these, from that of the cartilages of ossification, in this, that these last are crossed by many grey lines, and the others are not. When we cut the cartilages of ossification in any direction whatever, their divided surfaces exhibit numerous small points which are the cut extremities of these lines, which appear to be vessels, that, without yet circulating blood, contain a fluid of a deeper colour than that of the cartilaginous texture.

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

As we advance in age, the cartilages become harder, stronger, and less elastic. The gelatine that nourishes them has a peculiar character; for we know that the glue made from young animals differs essentially from that made from old ones. The cooks know very well the difference there is between the foot of a calf and that of an ox for jelly. This difference in the substance which essentially composes the cartilages, and which is undoubtedly their nutritive matter, evidently indicates that it does not always remain in these organs, but that it is constantly exhaled and absorbed there, as the phosphate of lime is in the bones, the fibrin in the muscles, &c.

In the last years of life, ossification seizes upon all the cartilages; but it begins in an opposite manner in those of the cavities and in those of the articulations. In the first it is by the centre, in the second it is by their surface which corresponds to the bone, that it commences; in general it is much slower in the latter, and among these, it is slower in the moveable articulations than in the immoveable.

The cartilages of the larynx and the ribs are osseous in their centre at the age of thirty-six or forty years, and even before; they afterwards become more and more so; it is this that renders the section of the thyroid cartilage very difficult in the last periods of life.

In the great number of operations that I have shown to students, I have satisfied myself, that after sixty years, the bistoury of ordinary temper is almost always insufficient to make this section; it requires something much stronger. It is the ossification of the costal cartilages, which renders old people unable to make those great efforts of inspiration so common to young ones; with them the diaphragm especially acts. I attribute also to this early ossification of the cartilages of the cavities, an ossification which always accompanies the development of the vascular system, the greater frequency of caries in this sort of cartilages than in all the others. I know not why in the larynx the arytenoid cartilages are the most exposed to this affection; but in the opening of dead bodies, it is a constant fact, all the cases of laryngeal phthisis with caries, that I have observed in the dead body, have shown me this.

III. Preternatural Development of the Cartilaginous System.

The cartilaginous system, like the osseous, is often developed in organs to which it is naturally a stranger. But there is this difference, that this phenomenon appears to be an effect of age in the first, whereas in the second it is always the effect of disease. Nothing is more common than to find cartilaginous balls in scirrhous, cancerous tumours, &c.; in the middle of those frequent morbid productions, in which the parts have an appearance like lard, in the lungs, liver, &c. when enlarged. I do not know why the peculiar membrane of the spleen has a great tendency to be encrusted with gelatine; it is perhaps of all the organs, that in which the preternatural cartilages are the most frequent. It is usually by irregular scales that the cartilaginous development appears; sometimes it attacks the whole membrane, which then presents a convex surface analogous to the convex surfaces of the moveable articulations, which the peritoneum covers, as these are covered by the synovial membrane. Can the spleen, when thus cartilaginous externally, yield to the changes of size that it often undergoes? I know not.

We know that there are often moveable and loose cartilaginous substances in the articulations. Do they arise from the ossification of a portion of the synovial membrane? I presume they do; for we frequently see them hold to the cartilage by membranous expansions. I have seen in a dead body, within the last year, the portion of synovial membrane that goes from the fatty substance behind the patella, to the depression that separates the condyles of the femur, almost wholly cartilaginous. If during life it had been detached by the effect of the motions, it would have formed one of these moveable and loose cartilages. Besides, as I know but this fact which seems peculiarly applicable to this point, I can only offer conjectures, especially as we know that the synovial and serous membranes are of the same nature, and yet these last hardly ever become cartilaginous.

Moreover these productions follow entirely the ordinary progress of ossification. At first cartilaginous and without blood vessels, they soon acquire a red centre, then osseous, which extends from the centre to the circumference, and which sometimes terminates by seizing upon the whole cartilage; so that they are real bones. This last circumstance is however very rare. The state in which we most commonly find these productions, is that in which they are osseous in the middle, and cartilaginous at the circumference. I found one of them in the articulation of the pisiform bone, of the size of the head of a great pin, and which, in its whole thickness was harder than ivory.

FIBROUS SYSTEM.

The fibrous organs have not been considered by anatomists in a general manner; no one has yet made a system of them. Separately described with the parts in which they are found, they cannot, in the present state of science, present us any of those great views, so useful to the practice of medicine, which show us each organic apparatus resulting from the combination of different systems, to which analogous ones are found in the other apparatus; so that though very different as it respects their functions, these apparatus are yet subject to the same diseases, because similar systems enter into their structure.

I presented, two years since, various general views upon the fibrous membranes, which have opened the way; but these membranes are only a division of the fibrous system, which must be considered here more at length.

ARTICLE FIRST.

OF THE FORMS AND DIVISIONS OF THE FIBROUS SYSTEM.

Though all the fibrous organs have precisely the same nature, and though the same fibre enters into the composition of all, yet the forms which they assume are extremely various; it is this variety of form, joined to that of their position and their functions, which has given them a different denomination, and made us designate them by the name of tendons, aponeuroses, ligaments, &c.; for there is no general denomination for the whole system, no word which answers for example to that of muscle, nerve, &c. which in the muscular, nervous systems, &c. gives an idea of the organization, whatever may be the form of the organ. I shall not create a word, I shall be easily understood without it.

All the fibrous forms can be referred to two general ones; one of these is membranous, the other in fasciæ. The organ is broad and thin in the first; it is longer and thicker in the second. Thus the muscles, the nerves, the bones themselves exhibit alternately this arrangement in their conformation, as we see in the retina compared with the round nerves, in the muscular layers of the stomach and the intestines, compared with the muscles of locomotion, and in the bones of the cranium compared with those of the extremities.

I. Of the Fibrous Organs of a Membranous Form.