The Radio-Ulnar Articulation

In the foal the shaft of the ulna is attached to the radius above and below the interosseous space by the interosseous ligament. Below the space the two bones become fused before adult age is reached. Above the space the ligament usually persists, but may undergo more or less ossification in extreme old age. The transverse or arciform ligaments (Ligamentum transversum ulnare et radiale ulnæ et radii) consist of fibers which pass above the interosseous space from either border of the shaft of the ulna to the posterior surface of the radius. The proximal radio-ulnar articulation, formed by two small convex facets on the ulna and the corresponding facets on the posterior surface of the proximal extremity of the radius, is inclosed in the capsule of the elbow joint and does not require separate consideration. The distal extremity of the ulna fuses early with the radius, and is, therefore, regarded usually as a part of the latter.

Movement.—This is inappreciable, the forearm being fixed in the position of pronation.