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Section VI. Of The Fibro-Cartilaginous System

Article First - Of The Fibro-Cartilages In The Normal State

§ 271. By cartilages we usually understand all those hard substances found between the bones which cover their surfaces, and some other parts mentioned before, (§ 260.) But the substances placed between the bones differ much from each other. Hence we early perceived the necessity of dividing the cartilages into several classes, according to their texture, or at least we did not forget to remark that all have not exactly the same texture. Haasedi vides them into three classes: 1, the cartilages formed entirely of a dense cellular tissue; 2, the ligamentous cartilages, (C. ligamenlosÅ“) ; 3, the mixed cartilages, (C. mixta.) Bichat considers the second class as a distinct system, and he has given to it the name of fibro-cartilage — and has made three subdivisions of it, viz. 1. The membranous fibro-cartilages, as those of the nose, the ear, and the trachea. 2. The articular fibrocartilages., comprehending the loose interarticular cartilages, and those which adhere intimately to the bones by their two faces, as those found between the vertebrae and the ossa pubis. 3. The fibro-cartilages of the tendinous sheaths, which cover the bones in those places where the tendons glide over them. But it is unquestionably more exact to refer the first division to the cartilages properly so called, as they have the same structure. We ought also to add to the two subdivisions a third, that of the annular fibro-cartilages, which Bichat has not mentioned.

The best classification of the fibro-cartilages is one in respect to their form and situation, and which admits of their being divided into three classes : 1st. Those fibro-cartilages the two faces of which are either wholly or at least in a great part loose, and the edges of which are united to synovial capsules, the movable articular fibro-cartilages.

2d. Those which have one of their faces loose, and adhere to the bone by the other. These are, a. long and grooved, as the fibro-cartilages of the tendinous sheaths ; and b. or circular, as those which border the edges of the joints, and which may be termed the annular fibro-carlilages.

3d. Those which have both faces entirely attached to the bones between which they arc placed.

§ 272. The intermediate fibro-cartilages are found principally in those joints which are exposed to frequent and extensive friction, as that of the knee, of the clavicle, and of the lower jaw. They di\ide the articulation more or less completely into two parts, because they are parallel to the tAvo articular faces between which they are extended. They are united more or less distinctly by fibrous parts to the circumference of the capsule or to the articular cartilages. Still they always remain movable, so that they can change their situation in the different motions of the joints ; hence they diminish compression and the concussion experienced by the articular cartilages in motion. They are usually circular and bi-concave, that is thicker at the cncumference than the centre. But the seinilunar fibro-eartilages of the knee-joint are hollowed, and extremely thin on one of theh: edges. Only one is usually found in each articulation; but that of the knee is an exception in this respect, as it sometimes contains two.

§ 273. The fibro-cartilages of the tendinous sheaths cover the bones in those places where the tendons glide over them ; hence they generally have a long grooved form. They are developed in the periosteum, and are usually composed of interlaced fibres, the direction of which is contrary to that of the sheath itself and of the tendon. They are generally thin, but become much thicker m certain points, and vary m this respect in all parts of the same sheath. Where they are unusually thick, we observe a corresponding development of a fibro-cartilaginous or osseous tissue in the tendon which glides upon them. We may easily be convinced of tliis in the place where the tendon of the tibialis posticus passes under the head of the artragalus to be inserted mto the scaphoid bone. This arrangement, then, forms real articulations in those parts Avhere considerable friction takes place. Something similar is seen in the crucial Hgament of the first and second cervical vertebrae, where it passes behind the odontoid process of the second.

§ 274. The annular fibro-cartilages are composed of circular fibres, arranged arormd the circumference of the rounded articular cavities which admit of extensive motions, as those of the ossa ilia and the scapula. They always grow thinner from their base to their loose edge ; they coiifine the motions of the joint by deepening its ca\ity, but not so much as an edge of bone would.

§ 275. These fibro-cartilages, which adhere on both sides to the adjacent bones, are formed of fibres, the direction of which is perpendicular to the surfaces between which they are extended, and form the articulations called symphyses^ (§ 242.) Their form depends upon that of the osseous surfaces which they are intended to unite. Hence they are almost circular between the bodies of the vertebrae, irregular betAveen the sacrum and ossa ilia, and oblong and square between the ossa pubis. They are inserted m the &st tAvo cases by broad surfaces, and in the third by narroAv edges.

§ 276. The texture of the fibro-cartilages is composed, as their name indicates, of a cartilaginous and ofafibrous substance. These tAvo masses are easily distinguished from each other, and form more or less regular alternate layers. This arrangement is particularly well marked in the intervertebral fibro-cartilages. Here in fact there is much more of fibrous substance than in the other fibro-cartilages, and it forms white, concentric, and solid layers, between which a brownish cartilaginous substance seems deposited principally in the middle, while externally it is converted into real crucial ligaments. On the contrary, in the interarticular cartilages and in the cartilages of the tendinous sheaths, the cartilaginous substance exceeds the fibrous so much, that this latter is hardly perceptible, and we might say that it has been injected into the other, so that it does not seem so regularly arranged. These fibrocartilages then are allied still more closely with proper cartilages.

It is a general law that the fibrous substance in a given portion of the fibro-cartilage exceeds in a greater or less degree the cartilaginous substance. Thus in the fibro-cartilages of the vertebrae, as also those of the pubic and sacro-iliac symphyses, the cartilaginous substance gradually diminishes towards the circumference, and finally gives place entirely to the fibrous substance. Several interarticular cartilages, às those of the knee, are attached to the adjacent bones by fibres evidently ligamentous.

§ 277. The tissue of the fibro-cartilages, in relation to the organic systems which form it, does not materially differ from that of the cartilages and of the fibrous organs.

§ 278. The same remark may be made in regard to their properties, as they combine those of the two systems. The fibro-cartilages are as elastic, but less hard and more flexible, and less brittle than the true cartilages. Their extreme solidity causes them to tear with great difficulty. They retain the bones to which they are attached very firmly together, and favor the gliding of the tendons. This circumstance, added to ihi.s that they are but slightly sensible to outward impressions, renders them capable of resisting the influence of external agents longer than the bones. Thus we sometimes see the bodies of the vertebrae almost wholly destroyed by chemical or mechanical causes, as for instance by an aneurism of the aorta, while the intermediate fibro-cartilages which unite them remain almost untouched.

Some fibro-cartilages undergo periodical changes not seen in the real cartilages ; they become less dense, softer, and moister, and hence allow more motion in the parts which they unite. This is seen particularly in the fibro-cartilages of the pelvis during pregnancy.

§ 279. The fibro-cartilages in the early periods of life, notwithstanding their softness, resemble the cartilages which appear at a later period, because at this time the gelatinous substance much exceeds the fibrous substance in all parts of the body. This is proved by the intervertebral fibro-cartilages and that of the symphysis pubis. As the age progresses on the contrary, the fibrous substance predominates more and more over the cartilaginous. Hence, partly on this account, the fibro-cartilages are much softer and more flexible in infants than in old men, and hence too, in great part, the' stiffness attendant upon old age.

The ossification of the fibro cartilages in advanced age is not rare. In fact the vertebrae are often united with each other by means of an osseous substance ; but this union depends more rarely on the ossification of the fibro-cartilages than on the formation of layers of bone on the circumference of the two faces which look towards the bodies of the vertebrae. But we have sometimes observed ossification of the intervertebral fibro-cartilages, and have then found on dividing the vertebral column longitudinally, that several vertebras were fused together, and were blended in one mass. The same is true of the symphysis pubis, and the sacrum is often united with the ossa ilia.

Article Second - Of The Fibro-Cartilages In The Abnormal State

§ 280. îh respect to morbid alterations, the fibro-cartilages resemble the cartilages and fibrous organs, in the nature of which they equally participate. They are but slightly subject to disease ; yet the observations of Palletta(l) and Brpdie(2) establish that inflammation and suppuration sometimes affect them, even before attacking the bones with which they are connected,

§281. We not unfi-equently see a substance perfectly resembling the fibro-cartilaginous tissue formed in some parts of the animal economy. This substance most generally assumes the form of round masses, very distinct from the surroundhig mucous tissue and the substance of the organs. Such are the substances which grow in the internal genital organs of the female, and especially in the uterus, in old maidens ; these formations, usually termed schirrous, but wrongly, adhere but slightly to the substance of the uterus, generally project above its surface, and are easily extirpated ; when cut across, they are seen to be composed of different layers and always of two substances irregularly intermixed, the cartilaginous and the fibrous. These accidental productions have more tendency to ossify than the normal fibro-cartilages : but this tendency to become bone does not depend entirely upon their size. Bodies similar to them in every respect are met with, between the vagina and the rectum, in the ovaries, the bones, the thyroid and the thymuä glands, and more rarely under the skin.

(1) Advers. chirurg. prima, p. 189.

(2) In the Med. chir. trans., vol. iv., p. 258.