Occasionally a portion of the cellular substance, which is exposed to pressure of motion, as over a prominent portion of bone, assumes the appearance of a bursa, secretes a similar fluid, and is similarly affected in consequence of inflammation. These adventitious bursæ are met with in various situations. Bunion is a good example of such a bursa thickened from long-continued pressure. They are seen on the outer ankles of tailors, on the shins of boot-closers, on the forehead, point of the elbow, &c. Disease of the bursæ may occur from external injury, and they often become affected subsequently to disease of the neighbouring joint. If the action is violent, lymph is effused on the inner surface, or external to its cavity, causing considerable thickening. The sac is thus sometimes all but obliterated. Tumours, originally housemaid’s knee, aggravated by continued pressure, are met with over the ligament of the patella in almost a solid state. Occasionally the action terminates in suppuration, pus being effused to a greater or less extent into the cavity; and if allowed to remain or accumulate, the abscess extends, and frequently communicates with the neighbouring joint, which may not have been previously diseased. In chronic cases of enlarged bursæ, especially of the bursal thecæ of the tendons of the wrist or ankle, we not unfrequently meet with loose cartilaginous bodies of various sizes, and of a flattened oval form, floating in the accumulated fluid. These have been also supposed to be formed by portions of lymph which have been deposited on the surface, condensed in structure, and afterwards become detached.