ELBOW JOINT. 123 



communis digitorum, extensor carpi ulnaris, anconeus, and supi- 

 nator brevis ; and behind, the triceps. 



Actions. The movements of the elbow joint are flexion and 

 extension, which are performed with remarkable precision. The 

 extent to which these movements are capable of being effected, is 

 limited, in front by the coronoid process, and behind by the ole- 

 cranon. 



6. The Radio-ulnar Articulation. The radius and ulna are firmly 

 held together by ligaments which are connected with both extre- 

 mities of the bones, and with the shaft ; they are, the 



Orbicular, Anterior inferior, 



Oblique, Posterior inferior, 



Interosseous, Interarticular fibro-cartilage. 



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 strongest behind where it receives the external lateral ligament, 

 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 dislocation of the 

 head of the radius. 



The oblique ligament is a narrow slip of ligamentous fibres, 

 descending obliquely from the base of the coronoid process of the 

 ulna to the lower part of the tuberosity of the radius. 



The interosseous 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 pos- 

 terior interosseous 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 intgrosseous ligament is in relation, in front, with the flexor 

 profundus digitorum, the flexor longus pollicis, and pronator quad- 

 ratus muscle, and with the anterior interosseous artery and nerve ; 

 and behind with the supinator brevis, extensor ossis metacarpi 

 pollicis, extensor primi internodii pollicis, extensor secundi inter- 

 nodii pollicis, and extensor indicis muscle, and near the wrist with 

 the anterior interosseous artery and posterior interosseous nerve. 



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

 transversely between the radius and ulna. 



The posterior inferior ligament is also thin and loose, and has the 

 same disposition on the posterior surface of the articulation. 



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

 ligament between the lower 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 



