The internal structure varies much in appearance; generally it is brown and soft, in some places broken down and mixed with a dark-coloured fluid, or with gelatiniform matter; sometimes it is much more dense, and resembles cartilage; in others, the cavity contains an ichorous fluid, mixed with small portions of more solid matter; in the advanced stage of the disease, the contents are often of the encephaloid nature, either in its homogeneous and solid form, or softened, broken down, and mixed with blood, or with a lard-like substance. Sometimes the cancelli of the bone are not destroyed, but extended, forming numerous cavities of considerable size, in which the morbid matter is deposited; in other instances, there is no appearance of cancellated structure, and the diseased mass contains rough osseous spicula, some detached, some loosely connected with each other, and others projecting from the inner surface of the bony parietes of the tumour. At the commencement of the disease, the patient feels acute pain in the part, the constitution is disturbed; afterwards, the pain becomes more dull, and there is a considerable swelling externally, which feels hard, and slightly elastic; in the advanced stage, the pain again becomes severe, and is of a lancinating kind, and the system is much deranged, the tumour is softer, often presents a sense of distinct fluctuation, and on being freely handled, is found to crepitate, in consequence of the loose spicula of bone rubbing upon each other. Ultimately, the integuments become tense, livid, or dark-red, ulcerate, and allow a portion of the softened tumour to protrude, in the form of a frightful fungus; there is profuse discharge, thin, and sometimes bloody; there is much constitutional irritation, and the patient is greatly exhausted. Not unfrequently, during the progress of the disease, especially in the long bones, fracture occurs at the diseased part, either from external injury, or sudden muscular exertion. This occurred in the case from which the specimen here delineated was obtained some months before the patient submitted to amputation. The morbid structure had not broken through its periosteal investment. The muscles and their interfilamentous tissue were sound. The patient remained free from any return of the local disease. Bones so affected, when broken, do not unite, the movement of the loose and rough ends is a cause of much irritation: inflammatory action is kindled in the morbid structure, suppuration occurs, the integuments give way, and ulcerate to a greater or less extent, and the advancement of the disease is thus much hastened. The tumour may be safely pronounced malignant; it is true, that for some time it shows no tendency to involve the adjoining soft parts, further than by the effects of inflammation induced by its pressure; but then it is limited by the external lamina of the bones, which confines it to the tissue in which it originated; but after this barrier has