What are cannon bones in artiodactyl legs?

In artiodactyls, cannon bones are formed by the fusion of the two principal metacarpal (in the forelegs) or metatarsal (in the hindlegs) bones. This structural adaptation is a result of the artiodactyl method of limb support, which relies on the third and fourth toes.1

By lengthening the lower limb bones and fusing these midfoot elements, artiodactyls achieve greater efficiency for movement. While most living artiodactyls possess both front and rear cannon bones, the extent of this fusion can vary; for instance, in camels, the fusion does not extend to the bottom of the bones, and their lower articular surfaces are less pulley-like than those found in ruminants. This evolutionary trend toward simplified, elongated limb extremities helps these mammals maintain speed and stability in open environments.1