CARPO-METACARPAL JOINTS 209 



The interosseous ligaments cannot be seen at present, but can be studied 

 later when the bases of the metacarpal bones are separated from each 

 other. 



ARTICULATIONES CARPOMETACARPE^: (CARPO-METACARPAL 

 JOINTS). 



The metacarpal bone of the thumb articulates with the greater 

 multangular bone by a joint which is quite distinct from the 

 other carpo-metacarpal articulations. An articular capsule 

 surrounds the joint, and is sufficiently lax to allow a very con- 

 siderable range of movement. On the dorsal and lateral 

 aspects of the articulation it is specially thickened. Its cavity 

 is distinct from that of the adjacent articulations. 



The medial four metacarpal bones are connected to the carpus 

 by volar and dorsal ligaments, and by one interosseous ligament. 



Each of these metacarpal bones, with the exception of the 

 fifth, possesses, as a rule, two dorsal ligaments and one volar 

 ligament. The articulation of the fifth metacarpal bone is 

 also closed on the medial side by ligamentous fibres. 



The interosseous ligament springs from the contiguous distal 

 margins of the capitate and hamate bones, and passes to the 

 medial side of the base of the third metacarpal bone. 



Dissection. To display the interosseous ligament, divide the 

 bands which connect the bases of the third and fourth metacarpal 

 bones, and sever the dorsal ligaments which bind the medial two 

 metacarpal bones to the carpus. The metacarpal bones thus set 

 free can then be forcibly bent volarwards, when the ligament in 

 question will come into view. 



Synovial Membranes of the Carpal, Carpo-metacarpal, and 

 Intermetacarpal Joints. The articulation between the pisi- 

 form and the triquetral bones and the carpo-metacarpal joint 

 of the thumb both possess separate capsules ; but the various 

 ligaments of the intercarpal, carpo-metacarpal, and proximal 

 intermetacarpal joints, though they are spoken of individually 

 as separate ligaments, constitute collectively a single capsule, 

 which surrounds a continuous joint cavity. The synovial 

 stratum of the capsule is prolonged over all parts of the 

 bones, enclosed within the capsule, which are not covered by 

 articular cartilage, and it is continued proximally between 

 the three bones of the proximal row of the carpus as far as 

 the interosseous ligaments which connect the bones together. 

 It covers the distal surfaces of those ligaments and is 



VOL. i 14 



