Fibro-carlilages dry readily when exposed to the air and become of a deep yellow colour ; they resist for a very long time, many months, the influence of maceration, and by long-con tinued boiling they become converted into a gelatinous substance. Their chemical conipo sition is said to be made up of albumen, phos phate of lime, chlorurcts of sodium and of potassium, sulphate of lime and other salts, usually found in animal textures.
The microscopic characters of fibro-cartilage do not seem to have been investigated with the same care as those of many other textures. I have examined by transmitted light very thin slices of the fibro-cartilages in the knee and temporo-maxillary joint, and the appearance presented was uniformly that of a very compli cated cellular structure, composed of minute meshes, very irregular in size and shape. In examining the intervertebral substance I have distinctly seen, towards the circumference of the disc, those fine and uniform cylindrical fibres with wave-like bendings described and figured by Jordan ;* but towards the centre the texture exhibited the cellular appearance with larger meshes, similar to that seen in the fibro cartilages of the knee and joint of the lower jaw.t Of the structures placed by Bichat among the fibro-cartilages, some have been considered by Meckel, Beclard, Weber, and other anato mists to be pure cartilage, and as it seems to me with much justice. These are the membra niform cartilages of the external ear, Eustachian tube, nose, larynx, trachea, and eyelids. The cartilaginous nature of most of these textures is very apparent upon carefully dissecting off the dense perichondrium which invests them, and to which, doubtless, they owe their flexi bility, or more correctly, by which they are prevented from being fractured under the influence of a bending force. Careful micro-. scopic observation may assist materially in affording marks indicative of pure cartilage ; and as the observations of Purkinje, and Aliescher approach in some degree to this object, I have thought it not foreign to the subject of this article to introduce here some account of these researches. The results of Purkinje's examinations of the minute structure of bone as well as cartilage were published in the year 1834 in an inaugural dissertation by Deutscli.j Mailer and Niescher have further investigated the subject and confirmed the statements of Purkinje.§ In examining thin slices of cartilage under the microscope by transmitted light, Purkinje observed numerous little bodies irregularly dis persed through its texture, of a round or oval form, and somewhat less transparent than the intervening substance. The annexed figure, taken from Miiller's work already referred to, gives a representation of these bodies: they are minated by Purkinje cartilaginous corpuscles (Knorpel Korperchen).
In some cases, as in porary cartilage, they peared to consist of nute granules ; they sented this appearance likewise in the nous part of the cranium of a frog. In the costal cartilages they were solid, and in the cartilaginous fishes, as in the lamprey, their contents were of a soft or fluid consistence. According to Purkinje, these corpuscles are found in the temporary cartilages, in permanent cartilage, in cartilage which becomes ossified in old age, as that of the ribs and larynx, in the cartilages of the nose and septum narium.
According to Miescher there are two kinds of permanent cartilage, differing from each other as well by external characters as by in ternal structure ; one of these scarcely differs at all from the temporary cartilage, the other is very dissimilar in structure. The first class is at once distinguished by its azure whiteness and by its pellucid brightness, not unlike that of mother-of-pearl, from the second, which is yellowish in colour, not pellucid, and spongy in texture. To the former class belong all articular cartilages, those of the ribs,* that of the ensiform cartilage of the sternum, the thy roid, cricoid, and arytenoid cartilages, and those of the septum narium and aim nasi. All the cartilages of this class are characterized by containing the microscopic corpuscles above described, variously arranged in each form of cartilage, in some placed in clusters, in others closely aggregated together in one part and separated in another. It is interesting to ob serve that the temporary cartilage universally contains these corpuscles, and as all the carti lages we have described are more or less prone to ossification in advanced age, we are led to the inference, that these corpuscles thus de posited are characteristic of cartilage which admits of becoming ossified.t To the second class of cartilages belong those of the external ear, of the epiglottis, and the capitula of Santorini, connected with the apices of the arytenoid cartilages, which in the ruminants, the hog tribe, and others, are of con siderable size. Besides the characters already mentioned which distinguish this class of car tilage from the former, the microscope dis closes some further differences. " Placed under the microscope," says Miescher, " the cartilages of this class present a very delicate network, opaque, composed of small round meshes which are filled by a uniform, pellucid substance, and each generally contains a single corpuscle somewhat roundish or oblong." The cartilages that belong to this class are con trasted with those of the former, as being never transformed into bone.