1. The rotula, a sort of bony production of the sesamoid kind, attached to the tendon common to the extensors of the leg, represents a moveable pulley, intended to slide on that formed by the separation of the condyls of the os femoris. It protects the joint which it covers, and, in point of structure, use, and situation, greatly resembles the olecranon, from which it differs only in this, that, instead of being a continuation or process of the tibia as the olecranon is of the ulna, it is only attached to that bone by a strong and thick ligament which is inserted into its tuberosity. Hence it follows, that between the injuries of the one and the other, there must be a great analogy: and indeed most of the signs characteristic of fractures of the olecranon, are characteristic also of those of the rotula, and the treatment which, in such cases, is suitable for the former, differs but little from that required by the latter. § II. OF THE VARIETIES AND CAUSES. 2. Fractures of the rotula may, in general, assume any direction, transverse, longitudinal, or oblique: but the first kind occurs in practice much more frequently than the others; and so great indeed is the disproportion, that it has almost exclusively attracted the attention of authors, in the numerous forms of apparatus invented to retain the fragments. 3. A shattering of the bone, the effect of a violent blow; a contusion; an echymosis; an effusion of blood into the adjacent soft parts; one or more wounds of the soft parts, with or without an opening into the joint; a swelling, the degree of which varies greatly, according to the state of the fracture, and the disposition of the subject, but which is constantly present; a double division of the bone, one of which, being longitudinal, forms an angle with the other, which is transverse; and a concomitant fracture of the condyls of the os femoris, or of the tibia: such are the varieties and complications, of which the fracture under consideration is susceptible.