ARTICULATIONS 155 



(2) for the distal radio-ulnar joint, (a) a capsule, and (b} the 

 discus articularis. 



In addition there are other ligaments which pass between 

 the bodies of the two bones of the forearm, and are therefore 

 common to the two articulations, viz. the oblique cord and 

 the interosseous membrane. 



To expose these ligaments the volar and dorsal muscles of the forearm 

 must be completely removed. 



Ligamentum Annulare Radii (O.T. Orbicular Ligament). 

 This is a strong ligamentous collar which encircles the 



Olecranon 



Incisura radiahs . 



Transverse portion 

 ^ of lig. collaterale 

 ulnare 



Incisura semilunaris 



Lig. annulare Processus coronoideus 



FIG. 62. Annular Ligament of the Radius. 



capitulum radii and retains it in the incisura radialis of the 

 ulna. It forms four-fifths of a circle, and is attached by its 

 extremities to the volar and dorsal margins of the incisura 

 radialis. It is somewhat narrower distally than proximally, 

 so that, under ordinary circumstances, the head of the radius 

 cannot be withdrawn from it in a distal direction, and it 

 is braced tightly upwards towards the elbow, and greatly 

 strengthened by the anterior and posterior portions of the 

 capsule of the elbow-joint, and by the radial collateral liga- 

 ment which are incorporated with it along its proximal 

 border. Its distal border is loosely attached to the neck of 

 the radius by a prolongation of the stratum synoviale, which 

 is covered externally by a thin layer of fibrous tissue. 



The Capsule of the Inferior Radio-ulnar Joint. This 



