262 



THE ARTICULATIONS 



(a) The Superior Radio-ulnar Joint 



Class. — Diarthrosis. Subdivision. — Trochoides. 



The bones which enter into this joint (which is often included with the elbow- 

 joint) are, the ulna by its radial notch and the radius by the smooth vertical border 

 or rim on its head. There is but one ligament special to the joint, viz.: — 



Annular. 



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

 than the capsule of the elbow-joint, which encircle the head of the radius, re- 

 taining it against the side of the ulna. The bulk of these fibres forms about three- 

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

 of the radial notch; some few are continued round below the radial notch, and 

 form a complete ligamentous circle. 



The ligament is inseparably connected along its upper edge and lateral (i. e., its non- 

 articular) surface with the anterior, posterior, and lateral portions of the capsule of the elbow, 

 a few of the fibres of these portions, especially of the lateral, descending to be attached to the 

 neck of the radius. The lower part of the articulation is covered in anteriorly, posteriorly, and 

 laterally by a thin independent membranous layer, which passes from the lower edge of the 

 annular Mgament to the neck of the radius, strengthened on the lateral side by those fibres 

 passing down from the capsule. They are loose enough to allow the bone to rotate upon its 



Fig. 297. — Annulab Ligament. 

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



with the radius.) 



Capsule of elbow-joint 



Cushion of fatty tissue 



Membranous tissue joining the an- 

 nular ligament to the neck of the 

 radius 



Radius 



Annular ligament 



Capsule of elbow 



,,-/y: 



own axis (fig. 297). Medially and below the cavity is closed in by a loose membrane, the liga- 

 mentum quadratum, which passes from the lower border of the radial notch to the neck of the 

 radius. 



The synovial membrane is the same as that of the elbow-joint, and, after 

 lining the annular Hgament, passes on to the neck of the radius, and thence up to 

 the lower margin of the articular cartilage. 



The arterial and nerve-supply are the same as those to the lateral part of the elbow-joint. 

 Relations. — Beliind lies the anconeus and in front the lateral border of the brachialis. 



(b) The Mid Radio-ulnar Union 



Class. — Synarthrosis. Subdivision. — Syndesmosis. 



There are two interosseous ligaments which pass betweeen the shafts of the 

 bones and unite them firmly together, viz. : — 



1 



Oblique cord. 



Interosseous membrane. 



The oblique cord [chorda obli(iua] (figs. 293 and 298) is a fairly strong, narrow 

 band, which passes from the lower end of the rough lateral border of the coronoid 



