It>4 RADIO-ULNAR ARTICULATION. 



Fig. 9.* The orbicular ligament (annular , coronary) is a firm 



band several lines in breadth, which surrounds the 

 head of the radius, and is attached by each end to the 

 extremities of the lesser sigmoid cavity. It is strong- 

 est behind where it receives the external lateral liga- 

 ment, and is lined on its inner surface by a reflection 

 of the synovial membrane of the elbow joint. 



The rupture of this ligament permits of the disloca- 

 tion of the head of the radius. 



The oblique ligament (called also ligamentum teres 

 in contradistinction from the interosseous ligament) is 

 a narrow slip of ligamentous fibres, descending 

 obliquely from the base of the coronoid process of the 

 ulna to the inner side of the radius, a little below its 

 tuberosity. 



The interosseus ligament is a broad and thin plane 

 of aponeurotic fibres passing obliquely downwards from the sharp ridge 

 on the radius to that on the ulna. It is deficient superiorly, is broader 

 in the middle than at each extremity, and is perforated at its lower part 

 for the passage of the anterior interosseous artery. The posterior interos- 

 seous artery passes backwards between the oblique ligament and the upper 

 border of the interosseous ligament. This ligament affords an extensive 

 surface for the attachment of muscles. 



The interosseous ligament is in relation^ in front , with the flexor pro- 

 fundus digitorum, the flexor longus pollicis, and pronator quadratus mus- 

 cle, and with the anterior interosseous artery and nerve ; and behind with 

 the supinator brevis, extensor ossis metacarpi pollicis, extensor primi 

 mternodii pollicis, extensor secundi internodii pollicis, and extensor indicis 

 muscle, and near the wrist with the anterior interosseous artery and pos- 

 terior interosseous nerve. 



The anterior infenor ligament is a thin fasciculus of fibres, passing 

 transversely between the radius and ulna. 



The posterior inferior ligament is also thin and loose, and nds the same 

 disposition on the posterior surface of the articulation. 



The inter articular, or triangular fibro- cartilage, acts the part of a liga- 

 ment between the low^er extremities of the radius and ulna. It is 

 attached by its apex to a depression on the inner surface of the styloid 

 process of the ulna, and by its base to the edge of the radius. This fibro- 

 cartilage is lined upon its upper surface by a synovial membrane, which 

 forms a duplicature between the radius and ulna, and is called the mem- 

 brana sacciformis. By its lower surface it enters into the articulation of 

 the wrist joint. 



Jlctions. The movements taking place between the radius and the ulna 

 are, the rotation of the former upon the latter ; rotation forwards being 

 termed pronation, and rotation backwards supination. In these move- 

 ments the head of the radius turns upon its own axis, within the orbicular 

 ligament and the lesser sigmoid notch of the ulna ; while inferiorly the 



dius. 4. The external lateral ligament inserted inferiorly into (5) the orbicular Imn- 

 ;nent. 6. The posterior extremity of the orbicular ligament, spreading out at its insertion 

 into the ulna. 7. The anterior ligament, scarcely apparent in this view of the articula- 

 tion. 8. The posterior ligament, thrown into folds by the extension of the joint. 



* 1. Articular surface of olecranon process of the ulna. 2. Coronoid process. 3. Or- 

 bicular ligament surrounding the neck of the radius. 



