The olecranon fossa of the humerus accommodates the olecranon process of the ulna.

the olecranon fossa

The olecranon process is the part of the ulna that hooks around the bottom of the humerus and forms the elbow joint.

It is the site where the olecranon process of the ulna bone articulates with.

The bone that contains the olecranon fossa is the humerus, which is located in the upper arm. The olecranon fossa is a depression on the posterior side of the humerus that accommodates the olecranon process of the ulna when the arm is extended.