202 THE SUPERIOR EXTREMITY 



small capitulum of the ulna is received into the ulnar notch 

 on the medial side of the distal end of the radius. In 

 connection with these joints there are special ligaments 

 which retain the bones in apposition. They are (i) for 

 the proximal radio-ulnar joint, the annular ligament', and 

 (2) for the distal radio-ulnar joint, (a) a capsule, and (ti) 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. 



Dissection. To expose the oblique cord and the inter- 

 osseous membrane, remove, completely, the volar and dorsal 

 muscles of the forearm. 



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

 The annular ligament is a strong fibrous collar which 



Olecranon 



V 



Radial notch of ulna m _ u ______^__ 



Transverse portion 

 of ulnar collateral 

 ligament 



Semilunar notch 



Annular ligament Coronoid process 



FIG. 96. Annular Ligament of the Radius. 



encircles the head of the radius and retains it in the radial 

 notch of the ulna. It forms four -fifths of a circle, and is 

 attached by its extremities to the volar and dorsal margins of 

 the radial notch of the ulna. 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 head of the radius cannot be withdrawn from it in a distal 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 towards the elbow, and 

 greatly strengthened by the anterior and posterior portions 



