230 



THE ARTICl 'LA TIOXS 



(a) The Superior Radio-ulnar Joint 

 Class. — Diarthrosis. Subdivision. — Trochoides. 



The l)ones which enter into tliis joint are, the iihia hy its lesser sigmoid cavity, 

 and the radius hy the smooth vertical border or rim on its head. There is but 

 one ligament special to the joint, viz. : — 



Orbicular. 



The orbicular ligament consists of bands of strong fibres, somewhat thicker 

 than the lapsule of the elbow-joint, which encircle the head of the radius, 

 retaining it against the side of the ulna. The bulk of these fiV)res forms about 

 three-fourths of a circle, and they are attached to the anterior and posterior 

 margins of the lesser sigmoid cavity; some few are continued round below the 

 lesser sigmoid cavity, and form a complete ligamentous circle. The ligament is 

 inseparably connected along its upper edge and external (i.e. its non-articular) 

 surface with tlie anterior, posterior, and external portions of the capsule of the 

 elbow, a few of the fibres of these portions, especially of the external, descending 



Fig. 230. — Orbicular Ligamext. 



(The head of the radius removed to show the membranous connection of this ligament 



with the radius.) 



Capsule of elbow -joint 

 CusMon of falty tissue 



Membranous tissue joining the 

 orbicular ligament to the neck 

 of the radius 



RADIUS 



Orbicular ligament 



Capsule of elbow 



to be attached to the neck of the radius. The lower part of the articulation 

 is covered in by a thin independent membranous layer, which passes from the 

 lower edge of the orbicular ligament to the neck of the radius, strengthened on 

 the outer side by those fil)res passing down from the capsule. They are loose 

 enough to allow tlie ])one to rotate upon its own axis (fig. 230). 



Tlie synovial membrane is the same as that of the elbow, and, after lining the 

 orbicular ligament, passes on to the neck of the radius, and thence up to the 

 articular cartilage. 



The arterial and nerve-supply are the same as those to the outer i)art of the 

 elbow-joint. 



(h) The Mid Radio-ulnar Union 



There arc two interosseous ligaments which pass between the shafts of the 

 bones and unite them iinnly together, viz. : — 



Oblique ligament. 



Interosseous membrane. 



The oblique ligament (figs. 228 and 230 A) is a fairly strong, narrowband, 

 which i)asses from the lower end of the rough outer border of the coronoid process. 



