• Body

• Two extremities

The ulna is the inner of the two bones of the forearm with the palms turned upward. The upper end of the ulna is broader proximally and narrower distally. It is located more toward the little finger side of the forearm. Proximally the ulna has a bony process called the olecranon process which is a hook-like structure that fits into the olecranon fossa of the humerus. This prevents hyperextension and forms a hinge joint with the trochlea of the humerus. There is also a radial notch for the head of the radius and the ulnar tuberosity to which muscles attach. At the distal end of the ulna is the styloid process.

ARTICULATIONS OF THE ULNA

• Trochlea of the humerus, at the right side of the elbow as a hinge joint with the semilunar trochlear notch of the ulna.

• The radius, near the elbow as a pivot joint, this allows the radius to cross-over the ulna in pronation.

• The distal radius, where it fits into the ulnar notch.

• The radius along its’ length via the interosseous membrane that forms a syndesmosis joint, a fibrous joint between two bones.

• It is also called the poisidion.