Ulna

The ulna is the caudolateral bone of forearm, divide into three segments:

• Proximal extremity with the olecranon

• Body (shaft) of ulna

• Distal extremity with the head of ulna.

The development of ulna varies considerably between species due to the evolution of rotation movement in forearm:

• In human, the ulna is well developped due to an important rotational movement (pronation and suppination).

• In carnivores, the movement is quite limited but the radius and ulna remains separated.

• In the pigs, the rotation is prevented by firm soft tissue bridging the interosseous space.

• In horses and ox, there is no movement and the two bones are fused.