Metacarpal I

The metacarpal bones are typically five long bones at the distal end of the thoracic limb. They are sometimes called thoracic metapodium.

They are numerated in a mediolateral sequence from McI to McV.

The metacarpal bones have all the same segments:

• A proximal extremity (base) bearing an articular surface for the distal row of the carpal bones and additional facets towards its neighbours.
• A shaft (body) with a palmar and a dorsal surface, and medial and lateral borders.
• A distal extremity (head) with a trochlea that articulates with the proximal phalanx.

The number of metacarpal bones may be reduced. For example, in the horse, only the third ray (cannon bone) is functional, with second and fourth metacarpal bones (splint bones) bearing no weight.