210 THE SUPERIOR EXTREMITY 



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 medial four 

 intermetacarpal articulations. 



In some cases the interosseous ligament which connects 

 the base of the third metacarpal to the capitate and hamate 

 bones shuts off the articulation of the hamate bone with the 

 medial two metacarpal bones, and converts the articulation 

 of the hamate bone with the medial two metacarpal bones 

 into a separate segment of the carpo-metacarpal joint. 



Dissection. To display the articular surfaces of the carpo- 

 metacarpal articulations, the metacarpus should be detached 

 from the carpus. The interosseous ligaments between the carpal 

 bones of the second row, and also between the bases of the 

 medial four metacarpal bones, can likewise be demonstrated 

 by carrying the knife between the bones, and dividing the 

 ligaments. 



Articular Surfaces. The base of the metacarpal bone of 

 the index will be seen to be hollowed out for the reception 

 of the lesser multangular bone. On the lateral side it also 

 articulates with the greater multangular bone, and on the 

 medial side with the capitate bone. The base of the third 

 metacarpal rests against the capitate bone alone. The base 

 of the metacarpal bone of the ring finger rests upon the hamate 

 bone, but articulates slightly with the capitate bone also. The 

 fifth metacarpal bone articulates with the hamate bone (Figs. 

 73, 77, 9 8 > 99, I00 )- 



Movements of the Metacarpal Bones. The opposed saddle -shaped 

 surfaces of the greater multangular bone and the metacarpal bone of the 

 thumb allow free movement at that joint. Thus the metacarpal bone of the 

 thumb can be moved (i) dorso-laterally (extension); (2) volarwards and 

 medially (flexion) ; (3) medially towards the index (adduction) ; (4) laterally 

 (abduction); (5) medially across the palm towards the little finger (opposition); 

 (6) a combination of the above-mentioned movements, occurring one after 

 the other, constitutes circumduction. The muscles which operate on the 

 thumb are (i) the two special extensors, brevis and longus, and the 

 abductor pollicis longus, producing extension ; (2) the flexor pollicis brevis, 

 the opponens pollicis, and the adductor pollicis, producing flexion and 

 opposition, two movements which are similar in character ; (3) the 

 abductor pollicis longus and the abductor pollicis brevis, producing 

 abduction ; (4) the adductor pollicis and the first dorsal interosseous 

 muscle, which give rise to adduction. 



The metacarpal bones of the index and middle fingers possess very 

 little power of independent movement. The metacarpal bone of the ring 

 finger, and more especially the metacarpal bone of the little finger, are 

 not so tightly bound to the carpus. When the hand is clenched they both 



