The olecranon fossa is a deep triangular depression on the posterior side of the humerus, superior to the trochlea.

The olecranon fossa is located on the posterior side of the distal humerus.

[1][2] The joint capsule of the elbow attaches to the humerus just proximal to the olecranon fossa.

[2][5] The olecranon fossa is present in various mammals, including dogs.

[6] This article incorporates text in the public domain from page 212 of the 20th edition of Gray's Anatomy (1918)