In the foal the shaft of the ulna is attached to the radius above and
below the interosseous space by the =interosseous ligament=. Below the
space the two bones become fused before adult age is reached. Above the
space the ligament usually persists, but may undergo more or less
ossification in extreme old age. The =transverse= or =arciform
ligaments= (Ligamentum transversum ulnare et radiale ulnæ et radii)
consist of fibers which pass above the interosseous space from either
border of the shaft of the ulna to the posterior surface of the radius.
The proximal radio-ulnar articulation, formed by two small convex facets
on the ulna and the corresponding facets on the posterior surface of the
proximal extremity of the radius, is inclosed in the capsule of the
elbow joint and does not require separate consideration. The distal
extremity of the ulna fuses early with the radius, and is, therefore,
regarded usually as a part of the latter.
=Movement.=—This is inappreciable, the forearm being fixed in the
position of pronation.