1 62 THE UPPER EXTREMITY 



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 four medial 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 os capitatum and os hamatum, and passes 

 to the medial side of the base of the third metacarpal bone. 



Dissection. To display this ligament, divide the bands which connect 

 the bases of the third and fourth metacarpal bones, and sever the dorsal 

 ligaments which bind the two medial 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 articulations between the os 

 pisiform and the os triquetrum as well as 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 membrane 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 these 

 ligaments and is excluded by them from the radio-carpal joint. 

 It passes also between the four bones of the distal row of the 

 carpus and covers the inner surfaces of the ligaments of the 

 carpo-metacarpal joints and the ligaments of the four medial 

 intermetacarpal articulations. 



In some cases the interosseous ligament which connects 

 the base of the third metacarpal to the os capitatum and os 

 hamatum shuts off the articulation of the os hamatum with the 

 two medial metacarpal bones, and converts the articulation 

 of the os hamatum with the two medial metacarpal bones 

 into a separate segment of the carpo-metacarpal joint. 



