IIAPIO-ULNAR. 



213 



ligaments, and forms a pouch between Fig. l33.-Left Elbow-Joint showing ; Posterior 



. , -, 1 and External Lateral Ligaments. 



the lesser sigmoid cavity, the internal 

 surface of the annular ligament, and the 

 circumference of the head of the radius. 



The Muscles in relation with the joint 

 are, in front, the Brachialis anticus; 

 behind, the Triceps and Anconeus; ex- 

 ternally, the Supinator brevis, and the 

 common tendon of origin of the Extensor 

 muscles; internally, the common tendon 

 of origin of the Flexor muscles, the 

 Flexor carpi ulnaris, and ulnar nerve. 



The Arteries supplying the joint are de- 

 rived from the communicating branches 

 between the superior profuncla, inferior 

 profunda, and anastomotic branches of 

 the brachial, with the anterior, posterior 

 and interosseous recurrent branches of 

 the ulnar, and the recurrent branch of the 

 radial. These vessels form a complete 

 chain of inosculation around the joint. 



The Nerves are derived from the ulnar, 

 as it passes between the internal condyle 

 and the olecranon ; and a few filaments 

 from the musculo-cutaneous. 



Actions. The elbow is one of the most 

 perfect hinge-joints in the body ; its move- 

 ments are, consequently, limited to flexion 

 and extension, the exact apposition of 

 the articular surfaces preventing the least 

 lateral motion. 



6. RADIO-ULNAE ARTICULATIONS. 



The articulation of x the radius with the ulna is effected by ligaments, which 

 connect together both extremities as well as the shafts of these bones. They may, 

 consequently, be subdivided into three sets : 1, the superior radio-ulnar ; 2, the 

 middle radio-ulnar ; and 3, the inferior radio-ulnar articulations. 



1. SUPERIOR RADIO-ULNAR ARTICULATION. 



This articulation is a lateral ginglymoid joint. The bones entering into its for- 

 mation are the inner side of the circumference of the head of the radius, which 

 rotates within the lesser sigmoid cavity of the ulna. These surfaces are covered 

 with cartilage, and invested with a duplicature of synovial membrane, continuous 

 with that which lines the elbow-joint. Its only ligament is 



THE ANNULAR OR ORBICULAR. 



The Orbicular Ligament (fig. 133) is a strong flat band of ligamentous fibres, 

 which surrounds the head of the radius, and retains it in firm connection with the 

 lesser sigmoid cavity of the ulna. It forms about three-fourths of a fibrous ring 

 attached by each end to the extremities of the sigmoid cavity, and is broader at the 

 upper part of its circumference than below, by which means the head of the radius 

 is more securely held in its position. Its outer surface is strengthened by the ex- 

 ternal lateral ligament of the elbow, and affords partial origin to the Supinator 

 brevis muscle. Its inner surface is smooth, and lined by synovial membrane. 



Actions. The movement which takes place in this articulation is limited to 

 rotation of the head of the radius within the orbicular ligament, and upon the 



