olecranon fossa olecranon fossa 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. olecranon fossaleft humerus. posterior view (olecranon fossa visible at bottom center)left humerus. posterior view (olecranon fossa visible at bottom center)detailsidentifierslatinfossa olecranita98a02.4.04.024ta21204fma23450anatomical terms of bone 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 olecranon fossa elbow joint. deep dissection. posterior view. elbow joint. deep dissection. posterior view. elbow joint. deep dissection. posterior view.