Triquetral bone months (4 years and 2 months). 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
Carpal bones or "distal surfaces" are articular, the superior generally convex, the inferior concave; the "medial" and "lateral surfaces" are also articular where they are in contact with contiguous bones, otherwise they are rough and tuberculated. The structure in all is similar: cancellous tissue enclosed in a layer of compact bone. Occasionally accessory bones are found in the carpus, but of more than 20 such described bones, only four (the central, styloid, secondary trapezoid, and secondary pisiform bones) are considered to be proven accessory bones. Sometimes the scaphoid, triquetrum, and pisiform bones are divided into two. The carpal bones are ossified endochondrally