1. The human radioulnar articular disc is a shelf extended medially from articular cartilage on carpal facet of radius. 2. Its medial border is embedded in the wedge of vascular connective tissue which contains fine arcuate ligamentous bands joining the disc to the ulna and articular capsule. 3. The ventral and dorsal borders are loosely attached to short ligaments which go from radius to the inner surface of articular capsule. 4. These arrangements permit radius and disc to rotate on ulna freely during pronation and supination.