4. Concretions of the joints do not always assume the same aspect. They vary greatly as to number, size, figure, structure, &c. In general, these bodies exist singly; sometimes, however, two of them are found in the same joint, and then they may be extracted either at the same time, or in succession, as was once done by Desault. Some English surgeons have also met with two concretions, and Morgagni has found even twenty-five, in the same joint. 5. They vary also in size. The largest ever met with by Desault, was fourteen lines in its longest, and ten in its shortest diameter. Six lines diameter in every direction, was the measure of the smallest one that occurred in his practice. 6. Their figure is sometimes lenticular and smooth on both sides, sometimes unequal, rough in one part, even in another, concave on one side, convex on the opposite, sometimes marked around the circumference and sometimes not with reddish points, and having occasionally a stem of a cellular texture and of some length, as may be seen in a paper by Theden. They usually consist of a single mass, but are in some cases divided into several lobules united by a kind of ligaments, as in the fourth case related in the Journal of Surgery. Though most frequently detached and floating in the interior of the joint, they have yet been found adhering by means of small portions of cellular substance, loose and capable of being stretched, or tight, hard, and even of a ligamentous nature. 7. If, from the external figure, we pass to the structure of these bodies, we will find them existing in three different states. Sometimes purely cartilaginous, sometimes completely bony, they at other times partake of both these states, in which case a bony nucleus is covered with a cartilaginous crust. Out of five cases, recorded by Desault, three are of the first, and two of the third kind. Many authors have met with the second kind, particularly Morgagni, who has even found in the same joint, some bodies of a bony and others of a cartilaginous nature. Hence it appears, that this variety of structure is to be attributed to the longer or shorter standing of the disease, that every concretion must pass successively through these three states, and that there is a great analogy between the formation of such bodies and natural ossification. 8. If we examine a body of the third kind cut in two through the middle, we will find it red and vascular in the centre, like an epiphysis, even when it is floating in the joint perfectly loose and free from adhesion.