Ulna bone

Ulna
The ulna is the medial bone of the forearm (Fig. 9.49). Its
proximal end articulates with the humerus at the elbow
joint and with the head of the radius at the proximal radioulnar
joint. Its distal end articulates with the radius at
the distal radioulnar joint, but it is excluded from the wrist
joint by the articular disc.
The proximal end of the ulna is large and is known as
the olecranon process (Fig. 9.49); this forms the prominence
of the elbow. It has a notch on its anterior surface,
the trochlear notch, which articulates with the trochlea
of the humerus. Below the trochlear notch is the triangular
coronoid process, which has on its lateral surface
the radial notch for articulation with the head of the
radius.
The shaft of the ulna tapers from above down (Fig.
9.49). It has a sharp interosseous border laterally for the
attachment of the interosseous membrane. The posterior
border is rounded and subcutaneous and can be easily
palpated throughout its length. Below the radial notch
is the supinator crest that gives origin to the supinator
muscle.
At the distal end of the ulna is the small rounded head,
which has projecting from its medial aspect the styloid process