38. The ulna is surmounted, at its upper end, by a considerable appendix, curved before, where it corresponds to the articulation of the fore-arm, and is covered with cartilage; convex behind, where there is nothing to separate it from the external integuments, and is attached at its upper end to the strong tendon of the triceps muscle, which appears to be incorporated with it. This appendix resembles greatly, in its structure, form, and uses, the rotula, from which it would differ in nothing, if the inferior ligament of the latter were ossified, so as to form a bony continuity between it and the tibia. It is exposed to fractures, perfectly similar to those of the rotula, but which differs so essentially from the other fractures of the ulna, as to call for a separate examination. 39. The ancients appear to have had but little knowledge of fractures of the olecranon, respecting which they have transmitted nothing to us, unless with Dalechamps, we find cause to recognize a reference to this affection in the following passage of Paul of Egina: _Cubitus frangitur ... circa partem ad cubiti gilbum_. Most of the moderns have spoken of it only in a vague manner; no one has described with accuracy the signs which characterize it; and few have given satisfactory ideas on its treatment. Petit has not spoken of it separately, and Duverney, who concludes with it his article respecting fractures of the fore-arm, has but imperfectly described for it a bandage which is in itself equally imperfect. Bell does not give us, on this point, an exposition of either his opinions or his practice. Yet this fracture is by no means so rare as to justify the silence of authors, and its treatment merits a degree of attention beyond that which is requisite in most other fractures. § XIII. OF THE VARIETIES AND CAUSES. 40. The olecranon suffers fractures at its base and at its summit, but more frequently in the first, than in the second situation. The division, though very generally transverse, is sometimes oblique. Desault met with an instance of an oblique fracture of the olecranon in a man, who had sustained a violent blow on his fore-arm from a club. 41. The causes which produce it are, either muscular action, a circumstance that very rarely occurs, or the direct action of external bodies, which is by far the most common case. The reverse of this is true with regard to fractures of the rotula, which are almost always produced by the contraction of the muscles attached to that bone. 42. The olecranon has been at times separated from the ulna, by the act of throwing a stone with great force. In such cases, the fracture has been produced by the immediate action of the triceps muscle. This is the first mode of division.