The word cartilage is employed too vaguely. It designates, in the common acceptation, bodies whose organization differ essentially. The cartilages of the nose and those of the articular surfaces have certainly but a very remote analogy between them; it is necessary then to establish a line of demarcation. I have endeavoured to do it by making two systems of them; one comprehends the cartilages properly so called, the other, the fibro-cartilaginous substances, such as those that are between the vertebrÆ, those in the middle of some articulations, &c. As this last is a compound of the fibrous and cartilaginous system, I shall not treat of it until I have spoken of the fibrous system.
By thus limiting the sense of the word cartilage, it gives us the idea of a hard, elastic, white substance, having an inorganic appearance, though it has a real organization. We find this animal substance in different parts of the body; it is met with especially, 1st, at the articular extremities of the moveable bones; 2d, on the articular surfaces of the immoveable bones; 3d, on the parietes of certain cavities, which it contributes in great measure to form; such are the cartilages of the nasal partition, of the ribs, the larynx, &c. Hence three different classes, which exhibit varieties in their forms, in their organization, &c.
ARTICLE FIRST.
OF THE FORMS OF THE CARTILAGINOUS SYSTEM.
The forms of the cartilages vary according to the class to which the cartilage belongs.
I. Forms of the Cartilages of the Moveable Articulations.
In every moveable articulation, there is at each osseous extremity, a cartilage which covers this extremity, which facilitates by its suppleness the motion of the two bones, the very hard substance of which would occasion by friction too great a shock; which reflects by its elasticity a considerable part of the motion, thus made more extensive; which breaks, by yielding a little, the violence of the shocks the limbs experience, and which thus render these shocks less dangerous.
The general character of the internal conformation peculiar to these cartilages is that of being always less thick than broad, of having a thickness which is in the ratio of their breadth: so that the cartilages of the great articulations exceed in this respect two, three, or four times even, those of the smaller articulations; and these cartilages are moulded upon the articular forms and exhibit two faces and a circumference.
One of these faces adheres to the bone; it unites with it so intimately, that fractures take place any where else rather than here. The means of union are not exactly known; this is certain, that the cartilage is not an elongation, a continuation of the cartilaginous parenchyma of the bone; the fibres of this parenchyma are not continuous with those of the cartilages. If it really was so, by removing from a long bone, fresh and clothed with its cartilage, the phosphate of lime which penetrates it, we should see this continuity, the bone and the cartilage would not differ; now I have constantly observed that in this experiment the action of the acid detaches the cartilage from the bone, either in fragments or as a whole. We see the cartilaginous fibres of the bone deprived of its saline base, terminating evidently on the convex surface which the cartilage embraces; no solution of continuity has taken place. In general, the appearance of the cartilaginous parenchyma, separate from its calcareous portion, is wholly different from that of a true cartilage., I presume that this difference is owing to the quantity of gelatine, which is greater in the second than in the first. The action of the acids, especially the nitric, is the best means of separating a cartilage from its osseous head; maceration does not produce this phenomenon under a great length of time; in ebullition, as the gelatine melts, it is less apparent.
The surface of the cartilage opposite to the bone, is intimately united to the synovial membrane of the articulation. It borrows from it the polish which it has; for wherever these substances do not correspond to this membrane, they lose this character, as we see in the larynx, in the cartilages of the ribs, &c. Here the means of adhesion is an extremely compact cellular texture, which neither maceration nor dissection can remove in layers. As the synovial membrane is wholly formed from this texture, it appears that upon the cartilage it is only an elongation of that which, after having contributed to the structure of this organ, is condensed upon its surface and organized as a membrane.
The circumference of the cartilages of which we are treating, terminates insensibly upon the osseous surface; it ceases at the place, where the synovial membrane quits the bone to be reflected.
The two corresponding cartilages of a moveable articulation are so arranged and adapted to each other, that in the medium position of the articulation, they touch exactly at all their points; now we know that the medium position of an articulation is that in which the bone inclines in neither direction, in which all the muscles contracting uniformly and making an equal resistance, keep it equally from extension and flexion, from adduction and abduction, &c. &c. and hold it in the exact medium. It is this position which the limbs take, when the will does not direct the muscular effort, as for example, in the foetus, in sleep, in rest, &c.; this is what some convulsions produce, in which all the muscles of a limb are agitated with an equal effort, by an extraordinary influx of the nervous power, &c. In no other position does the contact of the two articular cartilages take place at all their points; one portion of the surface of each always pushes with more or less force the parts surrounding the articulation, and distends them. The softness of the cartilaginous texture renders less painful this pressure, which would be distressing in the great motions, if the bones preserved their hardness at the extremity of the lever which they represent.
The cartilaginous forms of which we are treating, besides these common characters, have others peculiar to each kind of moveable articulations.
1st. In the first kind, the convex crust which covers the osseous head, is thick in the centre, but not at the circumference. An opposite arrangement takes place in the concave crust which receives this head; often even as in the humerus, and the femur, the thickness of this crust is increased at its circumference by a fibro-cartilaginous band. In this way, the effort is borne unequally by the two cartilages; but the uniformity of contact is established.
2d. In the second kind, which differs from the first by the absence of the motion of rotation, though in general a convexity is also received into a concavity, the arrangement for both the cartilages is nearly the same. Yet if two convex surfaces slide upon each other, an example of which we have in the condyle of the jaw and the transverse apophysis, then the cartilage is constantly becoming thinner towards the circumference of each; but then an inter-articular cartilage, thick at the circumference, thin in the middle, supplies the place of this arrangement, and establishes at all points a contact, which, without it, would only take place at the centre.
3d. In the third kind, the cartilaginous crust which covers the prominences and depressions, which reciprocally receive each other upon the extremities of the two bones, exhibits nearly an uniform thickness, as we see at the elbow, the knee, &c.; so that the pressure comes equally upon the whole articular surface.
4th. In the fourth and fifth kinds, the cartilaginous crusts moulded on the form of the osseous surfaces, have also a thickness nearly uniform at all points; I have found upon the bones of an adult, that this thickness is a line and a half in the radio-cubital articulation and that of the atlas, and a line in the carpal and metacarpal articulations.
II. Forms of the Cartilages of the Immoveable Articulations.
The cartilages are found only in two kinds of immoveable articulations, viz. in those with surfaces in juxta-position and those with indented surfaces. They form in all a very thin layer, continued upon both bones which articulate together, arising from their osseous portion, like those described before, being of the same nature as it, and forming a band so much the more close as we advance in age.
On the head these cartilages are very numerous; those of the cranium have more thickness on the convex than on the concave side, hence the more rapid disappearance of sutures in the last than in the first direction.
Wherever they are found, they contribute to unite the bones which form the cavities; hence, as we have said, there is less danger for these from external bodies, since the motion lost then in part in their soft texture, produces a less effect than if the cavity was only one osseous piece.
It appears that these cartilages have much more affinity to the phosphate of lime, than those of the moveable articulations, which rarely ossify, whilst at an advanced age these always become osseous, of which the cranium especially furnishes us examples. I would observe however that the cartilages of the indented surfaces have much more tendency to ossification than those of the surfaces in juxta-position. At least it is more common to see the parietal bones united with the occipital and frontal, than to see the union of the ossa maxillaria, ossa palati, &c.
III. Forms of the Cartilages of the Cavities.
The cartilages of the cavities have two different forms according to the parts which they contribute to form. They are, 1st, long, as in the ribs; 2d, flat, as in the larynx, the nasal partition, &c.
All are covered on the exterior with a fibrous membrane like the periosteum, and in which different muscles are inserted. In order to see this membrane it is necessary to macerate the cartilage for a day or two; it then becomes white and very evident in its thickness, and the direction of its fibres. The cartilages of the cavities do not exhibit the numerous foramina which are seen in the bones, because the blood vessels do not penetrate them. But few eminences and depressions are observed in them. We can hardly consider their forms in a general manner, because destined to very different uses, they have but little resemblance in their conformation.
ARTICLE SECOND.
ORGANIZATION OF THE CARTILAGINOUS SYSTEM.
In examining a cartilage in its interior, it is difficult to recognize in it an organic texture; there is one however, which is composed of a peculiar texture and of common textures.
I. Texture peculiar to the Cartilaginous System.
The peculiar cartilaginous texture exhibits an interlacing of fibres so compact, that it appears at first view homogeneous, formed into a mass of gelatine, without order and without any particular direction. Yet with a little attention we distinguish longitudinal fibres, which are crossed by transverse and oblique ones.
These fibres are more apparent in the cartilages of the moveable osseous extremities than in the others. They have infinitely less suppleness than the fibres of the fibro-cartilaginous substances; thus these bend without breaking, whilst the first break when they are bent considerably; the place of the rupture is smooth, with but few inequalities.
The cartilaginous texture is remarkable for many characters which distinguish it from the others. Next to the osseous texture, no one so long resists putrefaction and maceration. In the midst of a dead body wholly putrid, we find this texture almost untouched, preserving its appearance, its structure, and even oftentimes its natural whiteness. The same thing is frequently seen in gangrenous limbs in the living body. I have kept cartilaginous substances a very long time in water, which have not become altered, except a little in their colour. It would require more than a year perhaps, to reduce them to that soft, mucous, liquid pulp, to which maceration reduces most of the organs.
The cartilaginous texture contracts under the very powerful action of caloric, like all the other textures; yet this phenomenon is not apparent in the thyroid cartilage on account of its thickness, nor in the cartilages that encrust the bones, on account of their adhesion to these bones. But if we cut one in fine layers, and the others in slices, and plunge them into boiling water, they crisp up immediately and with force.
Exposed to drying, the cartilaginous texture becomes yellow, acquires a semi-transparency analogous to that of the tendons and dried ligaments; it becomes hard, contracts, diminishes in size, and loses its elasticity as it becomes hard.
Ebullition also gives it at first a yellow colour, then it cracks it upon the articular extremities, breaks it in different places, and raises it by layers which it softens, and which finally it melts almost completely to a small residue, which does not appear to be gelatinous. The softening of the cartilaginous texture renders it much more fit to be dissolved by the digestive juices than it naturally is. Swallowed raw, the cartilages would remain a long time in the stomach, whilst they are very easily digested when cooked; this is one of the very great advantages of the boiling of meat. In different experiments made upon digestion, I have found portions of cartilages still untouched in the stomach of dogs, whilst the flesh was already reduced to a pulp.
In certain cases, the cartilaginous texture is singularly altered. In the diseases of the articulation of the hip, it assumes an aspect wholly different; it is a soft substance, like lard, with very distinct vessels, sometimes with very evident fibres, having a size double, quadruple what is natural, and filling the cotyloid cavity. I have observed that then they do not become yellow, do not melt by ebullition and consequently are not gelatinous. In the same diseases, I have found the cartilaginous texture, upon the femur and the ilium, not only ossified, but changed into a substance exactly like ivory; I have preserved these two pieces.
When the cartilages become osseous, there is developed in their middle a texture analogous to that of the texture of the cells of the bones, in which the interlaced fibres leave between them very distinct spaces, and in which is deposited a kind of medullary fluid. This observation is especially applicable to those of the cavities, of the larynx, of the thorax, &c.
II. Parts common to the Organization of the Cartilaginous System.
There is cellular texture in the cartilages, though the want of interstices between their fibres, renders it very difficult to distinguish it in a natural state; in fact the development of fleshy granulations in wounds in which they are concerned, ebullition which, after having removed the gelatine, leaves a membranous and cellular residue, prove abundantly the existence of this texture, which we see besides in a very evident manner in some morbid states, in which the gelatine less copiously deposited in the cartilages, ceases to give them their usual hardness and leaves there a soft texture, often like sponge.
We do not discover any blood vessels in the cartilages. The exhalant system circulates only white fluids in them; but as this system is continuous with the arteries of the neighbouring parts, when the organic sensibility is raised in it by morbid irritations, and it thus becomes in relation with the red globules of the blood, these globules easily pass into it, and hence the redness the cartilages then have, as we see in their inflammation, in wounds of them, &c. It is this same phenomenon that we observe upon an inflamed conjunctiva, &c. When the irritating cause has ceased, the sensibility resumes its natural type, the red globules then become heterogeneous to the cartilage, which again becomes white.
We are ignorant of the nature of the white fluids which usually circulate in the vascular system of the cartilages. These fluids very easily become the vehicle of the bile, or at least of its colouring matter, which is spread through the animal economy in jaundice. We observe almost uniformly, that in this disease the cartilages are of a yellow colour, like all the other parts; the colour is more evident on their surface than in their texture, though it exists there. By opening a moveable articulation, the bilious appearance is commonly found as great there as upon the skin. Besides, all the parts, which like them, receive but few or no red globules in the ordinary state, are also found very evidently coloured. The tendons, the conjunctiva, the internal membrane of the arteries, &c. are examples of this. I have remarked in two subjects whose thyroid cartilages were ossified in the middle, that the yellow colour was much brighter in the osseous than in the cartilaginous portion. I do not know that nerves have ever been traced in the cartilages.
ARTICLE THIRD.
PROPERTIES OF THE CARTILAGINOUS SYSTEM.
I. Physical Properties.
Elasticity is a property generally extended to all organic and inorganic bodies. Among the first, it appears, that vegetables are endowed with it in the greater number of their organs; that animals, almost all of whose parts are soft, have some which return to their original state after having been stretched or compressed. Among these, the cartilages hold one of the first ranks in man. Their elasticity is very great, especially in the adult age, when their consistence is between the softness, which characterizes them in childhood, and the hardness, which is their attendant in old age. These two last properties are in fact not favourable to the elastic power.
If we plunge a scalpel into a cartilage, the edges of the divided place re-act upon it and expel it. Pressed against a resisting body, the cartilaginous extremity of a long bone becomes flat and resumes its form when the compression ceases. The edges of the thyroid cartilage, when it is cut longitudinally in the operation of bronchotomy, immediately approximate each other. The division of the cricoid ring exhibits the same phenomenon. The cartilages of the last ribs, when forced in towards the abdomen, come out of themselves, &c. &c. All these phenomena are the evident result of an elastic power. Thus nature has placed the cartilages wherever, to produce her phenomena, there is a necessity of uniting a physical to the vital forces, as in the larynx, in the nasal septum, in order to produce a sort of vibration in the passage of the air, at the extremity of the ribs, in order to be the seat of a species of twisting necessary to the mechanical part of respiration, at the articular extremities, in order to diminish the force of blows, &c.
It appears that the vital activity renders this property greater, which however remains very apparent after death. I presume that this is owing to the great quantity of gelatine they contain. 1st. We know that this substance possesses it in a very high degree, as is proved by the tremulous motion of jelly after it has become cold, by the examination of various animal glues, &c. 2d. If by ebullition we remove this substance from the cartilages, the nutritive parenchyma remains flaccid and soft. 3d. As the gelatine diminishes in our organs, the elasticity in them is less, as we see by examining the decrease of this property from the cartilages in which it predominates, to the fibro-cartilaginous organs in which it is in a smaller proportion, and to the fibrous bodies in which it is still less. It must be confessed however that many very gelatinous bodies, exhibit but very slight traces of elasticity; the skin is an example of this, and so are the tendons. Can the same substance, as it is differently operated upon by the organic laws, become the seat of properties wholly dissimilar?
II. Properties of Texture.
The cartilages are perhaps of all the organs, those in which the extensibility and contractility of texture are the least developed. We see them rarely distended and elongated; they break first. Diseases do not exhibit in the larynx those dilations so common in the other cavities, even the osseous ones. When divided, the edges, far from separating as in the skin, in a muscle, &c. approximate each other, as we have seen, by the effect of elasticity; we might say that this last property was accumulated in the cartilages at the expense of those of texture.
III. Vital Properties.
The vital properties are also very obscure in them. There is no animal sensibility in the natural state; it is only when inflammation or some other cause raises their organic sensibility, a sensibility which their functions necessarily suppose, it is only then, I say, that the brain perceives painfully the different irritations of which these organs are the seat. This becomes manifest, especially when foreign bodies are formed in the articulations, which suffer from their presence or are insensible to them, according as they irritate or not by their position, the cartilaginous extremities. There is neither animal nor sensible organic contractility in the cartilages; the insensible organic or tone alone exists in them, and this not in a great degree.
The sympathies are obscure, almost wanting in the cartilaginous system. I do not know that in the acute affections of the different organs, we observe sympathetic phenomena of sensibility or contractility in them. They remain tranquil in the midst of the general derangement which affects the other systems in this sort of diseases. In chronic affections even, they experience but little alteration; examine, for example, comparatively, the body of a man that has died a violent death, which has left his organs untouched, and that of one who has died from phthisis, dropsy, cancer, &c. you will perceive between almost all their organs a striking difference; the aspect of the muscles, of the mucous and serous surfaces, of the vessels, the nerves, &c. is entirely changed by the slow alteration they have undergone in the second; in the midst of these alterations the cartilages are unchanged, their appearance is almost the same as in a natural state.
Character of the Vital Properties.
From what has been said, it is evident that the cartilaginous life can have but little activity, that all the morbid phenomena must be characterized in these organs by a peculiar slowness, and that inflammation, for example, must always have in the cartilages, as in the bones, a chronic progress; this is rendered very clear by the following experiment. Lay bare a cartilage, divide it, and afterwards bring it in contact with a portion of a muscle, the skin, &c. also divided at their surface; the reunion does not take place, or at least not until a very long time. Why? because the life of the muscle or the skin being much more active than that of the cartilages, the inflammation of the first organs will be much more rapid than that of the second, and consequently the first inflammatory period of one will correspond to the last of the others. Now the reunion is so much the easier as the inflammatory periods correspond the more exactly in the two divided parts that are in contact. Hence why two parts of the same organ unite much more easily than two surfaces belonging to different organs. Hence why the greater the analogy in the lives of the two organs, the greater the facility with which they unite; why the difficulties increase as the differences of life become greater. Two osseous surfaces in contact require thirty or forty days to unite; the two edges of a cutaneous wound unite in two or three days. If you attempt to render continuous two organs thus unlike in their mode of cicatrization, by putting them in contact, you will succeed but slowly. Cover with skin the osseous extremity of an amputated stump; this will be in a state of suppuration, before the bone has hardly begun to soften; thus good practitioners have abandoned these pretended unions by the first intention, so much boasted of, after amputation by the flap operation. These unions would no doubt take place, if the life of the organs which enter into the composition of the flap was the same. But with the diversity of these muscular, osseous, tendinous, cellular, nervous organs, &c. it requires a long time for all their lives to be placed as it were in equilibrium, and for these organs to agglutinate at their divided extremities. I have already observed that the division of inflammations into acute and chronic gives physicians an inexact idea; for the duration of the inflammatory phenomena in the organs is wholly relative to their degree of life. An inflammation of the cellular texture and of the skin is acute, when it lasts but a few days; it is chronic when it continues forty or fifty days; in a cartilage, this last period may be that of an acute inflammation, whilst a duration of many months is necessary to make it chronic, as the diseases of the joints exhibit frequent examples.
The natural functions, as well as the morbid affections, have this slowness of the vital phenomena of the cartilages. The constant composition and decomposition, which their nutrition supposes, is not rapid. It requires a long time for nutritive substances to combine with them. I am persuaded that in animals which die suddenly from the effects of a carbuncle and whose muscles, glands, membranes, &c. almost instantly penetrated with the deleterious principles by the nutritive motion of composition, present an aliment so injurious, I am persuaded, I say, that these injurious principles not yet having penetrated the cartilages, these might be digested without danger. It is to the slowness of the motion of decomposition that must be attributed the slowness of the resolution of cartilaginous swellings; for tumours are resolved by the same laws that decompose our organs, as they are formed by the same laws that preside over their composition.
The cartilages and the analogous organs, are to the other parts of the economy, as it respects their vitality, what the zoophytes and other animals with a capillary circulation only, are to the animals better organized, to those with a general circulation and those that have a heart with a double ventricle. As much as life considered in general in the series of beings that it animates, presents a difference in its activity, so much it differs in the same respect, examined in particular in the organs of each of these beings.
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 foetus. 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.
