WRIST JOINT 201 



contact with the distal surface of the articular disc. The 

 lunate bone at the same time crosses the bounding ridge on 

 the distal surface of the radius, and encroaches on the 

 territory of the navicular bone, whilst a considerable part of 

 the surface of the navicular bone leaves the radius and comes 

 into contact with the lateral part of the capsule. 



Stratum Synoviale. The synovial stratum of the radio- 

 carpal joint lines the fibrous capsule and it covers the proximal 

 surfaces of the two interosseous ligaments which complete the 

 carpal surface. Sometimes the articular disc is imperfect, 

 and in those cases the synovial stratum of the radio- carpal 

 joint becomes continuous with the synovial stratum of the 

 distal radio-ulnar joint. 



The nerve supply is derived from the volar and dorsal 

 interosseous nerves. 



Movements at the Radio-carpal Joint. The hand can be moved in 

 four directions at the radio -carpal joint. Thus we have (a) volar 

 movement, or flexion ; (b) dorsal movement, or extension ; (c) ulnar 

 movement, or adduction ; (d) radial movement, or abduction. In 

 estimating the extent of these movements in the living person the student 

 is apt to be misled by the increase of range which is contributed by the 

 carpal joints. Thus, flexion is in reality more limited than extension, 

 although by the combined action of both carpal and radio-carpal joints 

 the hand can be carried much more freely volarwards than dorsalwards. 

 Adduction, or ulnar flexion, can be produced to a greater extent than 

 abduction, or radial flexion. In both cases the extent of movement at 

 the radio-carpal joint proper is very slight, but the range is extended by 

 movements of the carpal bones. The styloid process of the radius 

 interferes with abduction. 



The muscles which are chiefly concerned in producing the different 

 movements of the hand at this joint are the following : (a] flexors the 

 flexor carpi radialis, the palmaris longus, and the flexor carpi ulnaris ; 

 (b} extensors extensor carpi radialis longus, the extensor carpi radialis 

 brevis, and the extensor carpi ulnaris ; (c) abductors, or radial flexors 

 flexor carpi radialis, extensor carpi radialis longus, abductor pollicis 

 longus, and the extensor pollicis brevis ; (d} adductors, or ulnar flexors 

 extensor carpi ulnaris and flexor carpi ulnaris. 



In addition, all the muscles whose tendons cross the volar aspect of the 

 joint can, under certain conditions, assist in the production of flexion, 

 and the muscles whose tendons cross the dorsal surface can assist in the 

 production of extension, 



ARTICULATIONES RADIO-ULNARES (RADIO-ULNAR JOINTS). 



At the two radio-ulnar joints, proximal and distal, the 

 movements of pronation and supination take place. At 

 the proximal joint the medial part of the head of the radius 

 fits into the radial notch of the ulna; at the distal joint the 



