THE EADIO-ULNAK JOINTS. 



327 



Olecranon 



Radial notcl 



Transverse 

 portion of 

 ulnar collateial 

 ligament 



milunar notch 



Annular ligament of the radius Coronoid process 



FIG. 308. ANNULAR LIGAMENT OF THE RADIUS. 



displacement of the head of that bone in a distal direction. The distal margin 

 of this ligament is not directly attached to the radius. 



The synovial stratum is continuous with that which lines the elbow-joint. It 

 closes the joint cavity at the distal unattached margin of the annular ligament, where 

 it is somewhat loosely arranged in its reflexion from the ligament to the neck of 

 the radius. The epiphyseal line at the proximal end of the radius is intra-capsular. 



Articulatio Radioulnaris Distalis. The distal radio-ulnar joint is situ- 

 ated between the lateral aspect of the head of the ulna and the ulnar notch 

 on the medial side of the distal 

 end of the radius. In addition, it 

 includes the distal surface of the 

 head of the ulna, which articulates 

 with the proximal surface of a tri- 

 angular articular disc by means 

 of which the joint is excluded from 

 the radio-carpal articulation. 



Discus Articularis. The tri- 

 angular articular disc (Figs. 309 and 

 311), besides presenting articular 

 surfaces to two separate joints, is 

 an important ligament concerned in 

 i binding together the distal ends of 

 the radius and ulna. It is attached 

 by its apex to the depression at the 

 lateral side of the root of the 

 styloid process of the ulna, and by its base to the sharp line of demarcation between 

 the ulnar notch and the carpal articular surface of the radius. 



Capsula Articularis. The fibrous stratum is very imperfect, and consists of 

 scattered fibres, termed the anterior and posterior radio-ulnar ligaments (Fig. 310). 

 These ligaments pass transversely between adjoining non-articular surfaces on the 

 radius and ulna, and are of sufficient length to permit of the movements of the 

 radius in pronation and supination. 



The synovial stratum completes the closure of the joint cavity. It forms a 

 loose bulging projection (recessus sacciformis), passing proximally between the distal 

 ends of the shafts of the radius and ulna, and it also clothes the proximal surface of 

 the articular disc (Fig. 311). The cavity of this joint is quite distinct from that of 

 the radio-carpal articulation, except when the articular disc presents a perforation. 



Between the proximal and distal radio-ulnar articulations there are two 

 accessory ligaments, viz., the chorda obliqua and the interosseous membrane, which 

 ' connect together the shafts of the radius and ulna. 



Chorda Obliqua. The oblique chord (Fig. 306) is a slender fibrous band of 

 very varying strength which springs from the lateral part of the coronoid process 

 of the ulna, and stretches obliquely distally and laterally to the radius where it is 

 attached immediately distal to the tuberosity of the radius. 



Membrana Interossea Antibrachii. The interosseous membrane of the fore- 

 arm (Fig. 3 06) is a strong 



R^^g^*^ _^ ea ; 1 f ul " a fibrousmembrane which 



#^j^, PH stretches across the 



ft?T Bfi^k. styloid P rocess of ulna interval between the 



\A^ I iBll^/ radius and ulna, and 



surface for ^s^ ^ISBp^S ^R^ is fi rm ty attached to 



Tr^fortendon^S^SF . Apex of articular disc the interOSSCOUS Crest 



of each. Distally it 

 extends to the distal 

 limit of the space be- 

 tween the bones, whilst 

 proximally it only reaches a point about one inch distal to the tuberosity of the 

 radius. A gap, called the hiatus interosseus, is thus left between its proximal margin 

 and the chorda obliqua, and through this the dorsal interosseous vessels pass back- 



surface for ^&i 

 navicular bone ^ 

 Groove for tendon 

 of extensor longtis 

 pollicis 



Apex of articular disc 

 Articular disc 

 Surface for lunate bone 



FIG. 309. CARPAL ARTICULAR SURFACE OF THE RADIUS, 

 AND ARTICULAR Disc OF THE WRIST. 



