The body is prismoid in form, and curved, so as to be convex in the longitudinal direction behind, concave in front.
It presents three surfaces: medial, lateral, and dorsal:
- The medial and lateral surfaces are concave, for the attachment of the Interossei, and separated from one another by a prominent anterior ridge.
- The dorsal surface presents in its distal two-thirds a smooth, triangular, flattened area which is covered in the fresh state, by the tendons of the Extensor muscles. This surface is bounded by two lines, which commence in small tubercles situated on either side of the digital extremity, and, passing upward, converge and meet some distance above the center of the bone and form a ridge which runs along the rest of the dorsal surface to the carpal extremity. This ridge separates two sloping surfaces for the attachment of the Interossei dorsales. To the tubercles on the digital extremities are attached the collateral ligaments of the metacarpophalangeal joints.