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Other Terms: Capitate bone, Os Magnum (Carpus), Os capitatum
This is the largest of the carpal bones being centrally located in the distal row. At its proximal end it forms a large rounded head which is separated by a noticeable constriction or neck from the base or body at the distal end. The dorsal and palmar surfaces are roughened by the attachment of ligaments. The dorsal surface is wider than the narrow ventral surface that has a distinct prominence. This ventral prominence provides attachment for the oblique head of the adductor pollicis muscle. The other surfaces are principally smooth, providing facets for articulation with neighboring bones.
The word capitate is derived from the Latin word caput for head. The suffix -ate translates as provided with, therefore this bone means, provided with a head. It is so named because its proximal end forms a smooth, round surface resembling a head. Historically, os magnum is another name for this bone.
The capitate bone articulates with seven bones: the scaphoid, lunate, trapezoid, hamate, and second, third, and fourth metacarpals. The smooth, rounded head articulates in the proximolateral concavity formed by the scaphoid and lunate bones. On the distolateral surface, a facet is formed with the trapezoid bone. The medial surface forms a notched facet for articulation with the hamate bone. The triangular distal surface articulates with the third metacarpal bone. Distolaterally, a concave strip forms an articular surface with the second metacarpal. Distally the dorsomedial angle forms a small facet for the fourth metacarpal bone.
Arising from a single center during the second postnatal month, the capitate is the first carpal bone to ossify.