From the evidence before us, therefore, and from observations made on the second species of accidental cartilage, to be mentioned by-and bye, we are inclined to admit two distinct sources froin which these loose cartilages may have commenced. One, a deposit in the cel lular tissue outside the synovial membrane; the other a deposit within this membrane. The ori gin of both being lymph, which becomes cartila ginous, and often proceeds to an osseous state.
b. Insulated cartilages are sometimes found in connexion with true serous cavities. They are seldom larger than a pea, rounded, floating, or attached by a pedicle to the inside of the sac, and, in some instances, distinctly outside it. Laennec often found them between the tunica vaginalis testis and the tunica albuginea, and on one occasion in the lining membrane of the lateral ventricles of the brain. Andral saw three of these bodies in the serous mem brane of the brain ; one of them floated loose and unattached in the sac of the arachnoid ; the other two were attached to the choroid plexus by a delicate cellulo-vascular prolonga tion. Ile also often found them in the peri toneum, sometimes perfectly isolated, at other times appended to the serous membrane.* 2. Accidental cartilages of incrustatton, occurring in plates, are very irregular in size and shape. They are most frequently found in fibro-serous membranes, as the dura mater, the pericardium, and the immediate coverings of the testis and spleen. Upon this last viscus they are seen more frequently than in any other situation whatsoever. Bichat supposed they were altered portions of the fibrous membrane, having so generally met with them where the latter existed. The subserous cellular tissue is the proper seat of them. We often find them between the middle and internal coats of ar teries, in what may likewise be called a sub serous cellular tissue. (See ARTERY.) It is exceedingly rare to meet with them under mucous membranes. Andral saw one solitary instance of a true cartilaginous mass developed in the submucous cellular tissue of the stomach. The subcutaneous cellular sub stance is likewise nearly exempt from them ; but the same experienced pathologist relates, that one of the lower extremities of a woman who died in La CharW in the year 1820, was affected with elephantiasis ; underneath the skin, and occupying the place of the muscles, which were reduced to a few pale fibres, was found an enormous mass of condensed hard cellular tissue, possessing, in many places, all the physical characters of cartilage. In all
these instances there is every reason to believe, from the closest examination, that the newly formed substance is developed at the expense of the cellular tissue alone, and that neither the fibrous nor the serous membranes are al tered, nor indeed any adjoining texture. These last seem to be replaced by the accidental for mation, but they are only absorbed to make room for it, and not transformed into the new substance. An exception must, perhaps, be made in favour of mucous membrane, which appears capable of undergoing this change. Laennec relates the case of a child, in the membranous portion of whose urethra he found a large calculus. The mucous mem brane of the part presented several patches, of the size and thickness of a man's nail, which appeared to him semi-cartilaginous, and were incorporated with, and formed part of, the mucous membrane. In like manner Beclard found the mucous membrane of the vagina, in a case of prolapsus uteri, studded over with cartilaginous spots ; and he observed a similar appearance on the prepuce of an old man, who had had phymosis from the time of birth.
What is the cause of these formations ? Most probably they have their commencement in some obscure inflammatory action. It is true we often find them where there is no other appreciable lesion whatsoever, nor any trace of inflammation in the neighbourhood ; but, on the other hand, they seem to be but a step re moved, in structure, from coagulable lymph, and are sometimes imbedded in it ; and the irritation and consequent inflammation pro duced by foreign bodies must be allowed to have occasioned them in the instances just related from Bichat and Beclard.
3. The irregular or amorphous masses which we sometimes see in the thyroid gland, ovaries, uterus, testes, brain, liver, lungs, spleen, kidneys, and heart, are supposed to differ from the preceding classes, not only in form, but in connexions and origin. They appear to be united by continuity of substance with the tissues in which they are developed, and, in fact, to be altered portions of them. But it is by no means proved that cellular tissue may not, even in these cases, be the nidus of such concretions, and that the organs have not rather been absorbed to make room for them, than transformed into them.