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A MANUAL OF ANATOMY 



THE RADIO-ULNAR JOINTS. 



The radius and ulna are united by a superior and an inferior 

 radio-ulnar joint, and there is an intermediate connection between 

 their shafts. 



Superior Radio-ulnar Joint. — This joint belongs to the class 

 diarthrosis, and to the subdivision trochoides. The articular sur- 

 faces are the deep inner part of the head of the radius, and 

 the small sigmoid cavity of the ulna. There is one ligament at 

 this joint, namely, the orbicular or annular ligament. This is a 

 strong fibrous band, which forms about 

 four-fifths of a circle, and surrounds 

 the circumference of the head of the 

 radius, which it retains in contact 

 with the small sigmoid cavity. Its 

 extremities are attached to the 

 anterior and posterior margins of the 

 small sigmoid cavity. The ligament 

 is smaller below than above, and so 

 it maintains the head of the radius in 

 position. Its lower border is attached 

 to the neck of the radius by loosely- 

 disposed fibres. It gives attachment 

 to (i) the external lateral ligament 

 of the elbow- joint externally, (2) the 

 outer fibres of the anterior ligament 

 anteriorly, and (3) a portion of the 

 posterior ligament posteriorly. 



The synovial membrane is con- 

 tinuous with that of the elbow- joint, 

 and lines the inner surface of the 

 orbicular ligament and upper part of 

 the neck of the radius. 



Muscular Relations. — Extensor carpi 

 radialis brevior and supinator radii 

 brevis. 



Arterial Supply. — The radial recurrent and posterior interosseous 

 recurrent arteries. 



Nerve-supply. — The musculo-cutaneous and musculo - spiral 

 nerves. 



Inferior Radio-ulnar Joint. — This joint belongs to the class 

 diarthrosis, and to the subdivision trochoides. The articular sur- 

 faces are the sigmoid cavity of the radius, and the outer side of 

 the head of the ulna. The ligaments are anterior and posterior, 

 and the triangular fibro-cartilage. 



The anterior and posterior radio-ulnar ligaments consist of scat- 

 tered fibres in front of and behind the joint, which are attached to 

 the adjacent portions of the radius and ulna. The bones, however, 



Fig. 218. — The Upper End 

 OF THE Ulna, and the 

 Orbicular Ligament. 



