part of part of zone of long bone zone of bone organ proximal epiphysis of ulna trochlear notch http://upload.wikimedia.org/wikipedia/commons/6/60/Gray212.png semilunar notch incisura semilunaris ulnae FMA:23619 incisura trochlearis semilunar notch of ulna incisura trochlearis ulnae The semilunar notch of the ulna (trochlear notch of ulna, greater sigmoid cavity) is a large depression, formed by the olecranon and the coronoid process, and serving for articulation with the trochlea of the humerus. About the middle of either side of this notch is an indentation, which contracts it somewhat, and indicates the junction of the olecranon and the coronoid process. The notch is concave from above downward, and divided into a medial and a lateral portion by a smooth ridge running from the summit of the olecranon to the tip of the coronoid process. The medial portion is the larger, and is slightly concave transversely; the lateral is convex above, slightly concave below. UBERON:0008449 Wikipedia:Trochlear_notch