Occasionally the aneurismal sac deviates from its usual structure and appearance. Sometimes osseous or calcareous matter is found deposited, to a greater or less extent, in the substance of the parietes of the sac, or between the laminæ of fibrin which it contains. The tumour may also occupy unexpected situations, occurring after fracture of the bones and laceration of an artery, and perhaps from more slight external injuries. A disease of bone, somewhat resembling aneurism in that tissue, will be afterwards noticed. OF ANEURISM BY ANASTOMOSIS. This disease is generally seated in the external cellular tissue. It has been supposed to attack occasionally the internal organs; and a case is related in which it was situated in the cellular tissue, between the vagina and rectum. Frequently the congenital marks of children, termed Nævi, degenerate into this disease: occasionally, though very rarely, it occurs in sound skin and in adults. A good case of this kind will be found in the _Practical Surgery_, p. 336. When the cutaneous tissue is involved, the colour of the tumour is a dark red, or inclining to purple; it is irregular on its surface, and has a soft, spongy feel. Often it is raised distinctly above the surrounding parts; at other times it is flat, scarcely prominent, and seems to enlarge chiefly in a lateral direction. The skin is then frequently unaffected; pulsation, in some instances, is perceived; often, however, the tumour is of an inactive character, affords no pulsation, and, on being handled, feels like a doughy, elastic intumescence, appearing to be composed of a congeries of distended vessels, in which the blood circulates slowly, and resembling varix. The tumour is formed by enlargement, tortuosity, and increased activity of the capillary and other vessels; in some cases the arteries are chiefly affected, in others the veins. That such is its structure, can be distinctly proved by dissection; the vessels are found enlarged to many times their natural size, and their coats are much attenuated; it is certainly not cellular, as some have supposed. The tissue is similar to that of the cavernous and spongy bodies of the penis, and has hence been named erectile. A natural structure of the same kind is met with in the lower animals in different situations. The tumour is much increased on the general circulation being hurried, as by crying in children, by fits of passion, by the excitement of ardent liquors or venery, and during or before the menstrual discharge. On such occasions the surface frequently gives way, hemorrhage ensues, and is often profuse; in females it sometimes takes the place of the regular discharges. The tumour, in general, increases rapidly in size, and bleeds from time to time; now and then, however, it becomes stationary, even in circumstances where it could hardly be expected, and remains so during the remainder of the patient’s life. Again, in children, the surface of the tumour is not unfrequently ulcerated,