Ulna

thumb|Right ulna, lateral aspect. (After Piersol.) thumb|Right ulnar bone, medial aspect. (After Piersol.)

The olecranon (, ), is a large, thick, curved bony process on the proximal, posterior end of the ulna. It forms the protruding part of the elbow and is opposite to the cubital fossa or elbow pit (trochlear notch). The olecranon serves as a lever for the extensor muscles that straighten the elbow joint.

bone in the arm

styloid process of the ulna

Dent of the ulna receiving the radius