Some years ago I saw an instance of a boy, about 13 years of age, who had his breast-bone much broken by a fall. On this account he was admitted into Guy’s Hospital; but not till a fortnight after the accident happened. Upon examination, there appeared an evident separation of the broken parts of the bone, which were removed at a considerable distance from each other: the intermediate space was occupied by a tumor of a considerable size: the integuments were of their natural complexion: the tumor had as regular a contraction and dilatation as the heart itself, or the aorta could be supposed to have. Upon pressure, the tumor receded; upon a removal of the pressure, the tumor immediately resumed its former size and shape. All these are the distinguishing signs of a true recent aneurism. The situation and symptoms of this swelling were judged sufficient reasons for considering the nature of the disease as uncertain; on which account it was left to take its own course. The event was, the tumor burst in three weeks after his admittance, discharged a considerable quantity of matter, and the patient did well. From what has been above advanced it is plain, if these arguments can be supported by facts, that the laying down such rules for infallibly distinguishing aneurismal tumors from tumors proceeding from very different causes, must be a matter of the greatest difficulty: and, as a further proof of their uncertainty, I take the liberty of offering the following short history of a remarkable case, which has lately occurred in my own experience. In the month of December 1756. John Yates, aged 35 years, received an hurt upon and about his knee, by falling upon the ground from a man’s back. The accident was immediately followed with a considerable degree of lameness and pain; which upon standing or walking were greatly increased. He continued in much the same state for about six weeks after the accident. At the end of this time, the calf or the leg was attacked with an œdematous or doughy swelling; which, in a fortnight, became so painful, as to disable him from walking. The tumor continued to increase for about eight weeks; and at length extended itself so far upwards, as to affect the greatest part of the thigh, the whole of which was attended with excessive pain, but more particularly so about the knee. _N. B._ So far I relate from the patient’s own account. On the 28th of April 1757. he was admitted into Guy’s Hospital under my care. Upon examination, the thigh appeared enlarged to a very great size. The tumor was uniform, and extended from the inside of the knee to within a very small space of the groin. The integuments were in every part of their natural colour. Upon pressing the tumor on the inside, it appeared soft, and there was a very evident fluctuation to be felt on its internal and lateral part; but there was not the least appearance of pulsation. The tumor, on its superior and posterior parts, was of a stony hardness.