140 ELBOW JOINT. 



The internal lateral ligament is in relation posteriorly with the ulnar 

 nerve. 



The external lateral ligament is a strong and narrow band, which de- 

 scends from the external condyle of the humerus, to be inserted into 

 the orbicular ligament, and into the ridge on the ulna, with which the 

 posterior part of the latter ligament is connected. This ligament is 

 closely united with the tendon of origin of the supinator brevis 

 muscle. 



The synovial membrane is extensive, and is reflected from the carti- 

 laginous surfaces of the bones upon the inner surface of the ligaments. 

 It surrounds inferiorly the head of the radius, and forms an articulat- 

 ing sac between it and the lesser sigmoid notch. 



The muscles immediately surrounding, and in contact with, the 

 elbow joint, are in front, the brachialis anticus ; to the inner side, the 

 pronator radii teres, flexor sublimis digitorum, and flexor carpi ulnaris ; 

 externally, the extensor carpi radialis brevior, extensor communis 

 digitorum, extensor carpi ulnaris, anconeus, and supinator 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 olecranon. 



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

 held together by ligaments which are connected with both extremities 

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



Orbicular, Anterior inferior, 



Oblique, Posterior inferior, 



Interosseous, Interarticular nbro-cartilage. 



The orbicular ligament (annular, coronary) is a firm band several 

 lines in breadth, which surrounds the head of the radius, and is attach- 

 ed 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 sarface 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 (called also ligamentum teres in contradistinc- 

 tion 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 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 pas- 

 sage of the anterior interosseous artery. The posterior interosseous 

 artery passes backwards between the oblique ligament and the upper 



