ulnaa

The ulna is one of the two long bones in the forearm, located on the medial side when the arm is in the anatomical position. It runs parallel to the radius, which is the other forearm bone. The ulna is the larger of the two bones and is primarily responsible for forming the elbow joint with the humerus, the bone of the upper arm. Specifically, the olecranon process of the ulna articulates with the trochlea of the humerus, allowing for flexion and extension of the elbow. The ulna also contributes to the wrist joint by articulating with the radius at its distal end, although its direct connection to the carpal bones is limited.

The proximal end of the ulna features the olecranon, which forms the point of the elbow, and the coronoid process. These structures provide attachment points for muscles involved in elbow flexion. The shaft of the ulna is roughly triangular in cross-section. At the distal end, the ulna has a head that articulates with the radius and a styloid process. While the radius is more involved in the wrist joint's articulation with the carpal bones, the ulna plays a supporting role and its distal end is separated from the carpal bones by a fibrocartilaginous disc. The ulna is essential for forearm stability and provides leverage for many hand and wrist movements.