In carnivores, the palmar sesamoid bones are two elongated, slightly curved small bony structures located on the palmar surface of each of the four main metacarpophalangeal joints, in the tendons of insertion of the interosseous muscles. They articulate primarily with the head of each metacarpal bone and secondarily with the palmar tubercles of the base of each proximal phalanx. Their truncated distal ends articulate by small facet with the palmar tubercles of the corresponding proximal phalanges. On digit I, there is a single proximal sesamoid bone.
They are numbered from medial to lateral, with the most medial sesamoid bone of the second metacarpophalangeal joint being sesamoid bone #1 and the most lateral sesamoid of the fifth metacarpophalangeal joint being sesamoid bone #8
In the first digit, there is usually just lonly one sesamoid bone.