=Ox.=—No important differences exist. The upper part of the interosseous
radio-ulnar ligament is commonly ossified in the adult.
=Pig.=—There are no important differences. The radius and ulna are so
firmly united by the interosseous ligament as to prevent any appreciable
movement between them.
=Dog.=—The joint capsule is reinforced in front by an oblique ligament
which arises on the front of the external condyle of the humerus above
the joint surface, and joins the terminal part of the biceps and
brachialis below. The external lateral ligament is thick and divides
into two parts; the anterior part is attached to the radius and blends
with the annular ligament; the posterior part widens below, forming a
sort of cap, and is attached to the ulna. The internal lateral ligament
also divides into two branches; the anterior branch ends on the inner
surface of the neck of the radius; the posterior enters the interosseous
space and is attached to both bones. An elastic band (Ligamentum
olecrani) extends from the outer surface of the internal epicondyle to
the anterior border of the ulna.
There are two radio-ulnar joints. The proximal radio-ulnar joint is
included in the capsule of the elbow, but is provided with an annular
ligament which extends from the lower part of the external ligament
across the front of the proximal end of the radius to the ulna, blending
with the biceps and brachialis tendons. The distal joint is formed by a
concave facet on the radius and a convex one on the radius, and is
surrounded by a tight capsule. The interosseous membrane unites the
shafts of the two bones. The movements consist of limited rotation of
the radius (ca. 20°), carrying the paw with it. The ordinary position is
termed pronation; outward rotation is supination.[40]