the disk that holds together the distal ends of the radius and ulna; it is attached by its apex to a depression between the styloid process and distal surface of the head of the ulna, and by its base to the ridge separating the ulnar notch from the carpal surface of the radius. Syn: discus articularis radioulnaris [NA], radioulnar disk, radioulnar articular disk, triangular cartilage, triangular disk of wrist, triquetrous cartilage(1).