The aneurismal tumour in general increases, and approaches the surface, involving and destroying all the intervening textures. If resisted in its enlargement by bone, even this is not sufficient to impede its progress; the bone is absorbed, and perhaps ulcerated, at the point where it is compressed by the tumour. The osseous is more liable to destruction from this cause than the cartilaginous tissue, contrary to what occurs from compression by abscess. Ultimately the sac gives way, and its contents are discharged either externally, or into an internal cavity or canal, in consequence of its parietes sloughing from the compression made by the tumour; and such termination is instantly fatal. [Illustration] An aneurism of the descending aorta, in a great measure one from dilatation, is here represented: the patient also laboured under popliteal aneurism of one limb, and inguinal of the other. He died suddenly, in consequence of the giving way of the internal tumour. The escape of blood into the cellular tissue may even take place to such an extent as to prove fatal in a few hours. The disease may also prove fatal by mere compression, as of the trachea, impeding breathing, and inducing disease of the respiratory organs; or by pressure on the gullet preventing the passage of food: in the latter case, however, the dissolution is generally more sudden, in consequence of the compressing part of the tumour giving way, and the contents being evacuated into the stomach or mouth. If the aneurism compress a plexus of nerves, or the spinal chord itself, the anterior part of the vertebræ having been previously absorbed, paralysis is produced. In consequence of aneurism, the circulation of blood in the vessel is obstructed; hence the collateral branches above the tumour become enlarged, and through them the circulation is continued; by their anastomosis with collateral branches which arise below the seat of the tumour, a portion of the fluid is brought back into the canal of the original artery. The circumstance of collateral enlargement used to be distinctly enough demonstrated in amputation, one of the old cures for the disease. The tumour may be suddenly increased by a portion of the parietes giving way, and the blood being propelled into the cellular tissue, which becomes thereby condensed, and supplies the deficiency in the original sac; diffuse is thus superadded to the true or encysted aneurism. The disease is generally accompanied with great pain, the neighbouring nerves being much stretched by the enlargement of the tumour, as in the axilla or ham; in these situations also the limb below the aneurism is much swollen from the compression of the absorbents and veins and consequent infiltration into the cellular tissue. Diffused aneurism from wounds, and the other species of the disease, will be afterwards treated of.