Elbow Joint

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.