<P> The head of the radius has a cylindrical form , and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus . The circumference of the head is smooth ; it is broad medially where it articulates with the radial notch of the ulna , narrow in the rest of its extent , which is embraced by the annular ligament . </P>
the head of the radius articulates with which structure and bone
the capitulum of the humerus