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120 where the muscles play freely over the exostoses, the cartilaginous matter may be esteemed as a provision of nature, intended to counteract, in some measure, the effects of friction.

True exostosis differs, then, from other bony tumours, in the appearance of its intimate structure. In malignant swellings of bone, there is an alteration to a greater or less extent in the structure of the original osseous tissue, and in the arrangement of its materials. In exostosis, the new formation does not visibly differ in texture from that of the original bone.

In the treatment of exostosis, the surgeon must be guided very much by the site of the disease, the inconvenience it gives rise to, and the deformity it occasions. When an exostosis is situate on the parietal bones, on the lower jaw, or on one of the long bones, and is evidently on the increase, it should be removed; for, if allowed to remain, the irritation occasioned on the skin from the pressure of a hat, or other articles of dress, is apt to prove exceedingly troublesome. But when the exostosis is not increasing in size, and is situate upon a bone which is well covered by flesh, the practitioner should hesitate, and avoid