The olecranon fossa is a deep triangular depression on the posterior side of the humerus, superior to the trochlea. It provides space for the olecranon of the ulna during extension of the forearm. Structure The olecranon fossa is located on the posterior side of the distal humerus. The joint capsule of the elbow attaches to the humerus just proximal to the olecranon fossa. Function The olecranon fossa provides space for the olecranon of the ulna during extension of the forearm, from which it gets its name. Other animals The olecranon fossa is present in various mammals, including dogs. Additional images References External links Photo of model at Waynesburg College skeleton3/olecranonfossa () Imaging at umich.edu Bones of the upper limb Humerus