The triquetrum (triangular) may be distinguished by its pyramidal shape, and by an oval isolated facet for articulation with the pisiform bone. It is situated at the upper and ulnar side of the carpus. The superior surface presents a medial, rough, non-articular portion, and a lateral convex articular portion which articulates with the triangular articular disk of the wrist. The inferior surface, directed lateralward, is concave, sinuously curved, and smooth for articulation with the hamate. The dorsal surface is rough for the attachment of ligaments. The volar surface presents, on its medial part, an oval facet, for articulation with the pisiform; its lateral part is rough for ligamentous attachment. The lateral surface, the base of the pyramid, is marked by a flat, quadrilateral facet, for articulation with the lunate. The medial surface, the summit of the pyramid, is pointed and roughened, for the attachment of the ulnar collateral ligament of the wrist.
The triquetrum articulates with three bones: the lunate laterally, the pisiform in front, the hamate distally; and with the triangular articular disk which separates it from the lower end of the ulna.