CARPO-METACARPAL JOINTS. 279 
INTERMETACARPAL JOINTS. 
The four inner metacarpal bones articulate with each other at their proximal 
ends or bases, between the opposing surfaces of which joint cavities are found— 
arthrodial diarthroses. These cavities are continuous with the carpo-metacarpal 
joint (not yet described), and hence the ligamentous arrangements only enclose 
three aspects of each joint. 
Three strong transverse ligaments (Figs. 216 and 217) bind adjacent palmar, 
dorsal, and interosseous areas of the bases of the metacarpal bones, and hence they 
are called ligamenta basium (oss. metacarp.) volaria, dorsalia et interossea. A 
synovial membrane is associated with each of these joints, but it may be regarded 
as a prolongation from the carpo-metacarpal articulation. 
CARPO-METACARPAL JOINTS. 
The articulation of the metacarpal bone of the thumb with the trapezium 
differs in so many respects from the articulation between the other metacarpal 
bones and the carpus, that it must be considered separately. 
(A) The articulatio carpo-metacarpea pollicis (Figs. 216 and 217) is the joint 
between the infero-external surface of the trapezium and the superior surface of 
the base of the first metacarpal bone. Both of these surfaces are saddle-shaped, 
and they articulate by mutual co-aptation. 
The joint-cavity is surrounded by a fibrous capsule, in which we may recognise 
palmar, dorsal, external, and internal lateral bands, the last being the strongest and 
most important. 
Synovial membrane lines the capsule, and the joint-cavity is isolated and quite 
separate from the other carpal and carpo-metacarpal articulations. 
At this joint movements occur about at least three axes. Thus, around a more or less trans- 
verse axis, flexion and extension take place ; in an antero-posterior axis abduction and adduction 
(movements which have reference to the middle line of the hand) are found ; while a certain 
amount of rotation is possible in the longitudinal axis of the digit. The very characteristic 
movement of opposition, in which the tip of the thumb may be applied to the tips of all the 
fingers, results from a combination of flexion, adduction, and rotation, and by combining all the 
movements possible at the various axes, a considerable degree of cireumduction may be produced, 
in spite of the fact that this is not a ball-and-socket joint. 
(B) The articulationes carpo-metacarpee digitorum are the joints between 
the bases of the four inner metacarpal bones and the four bones of the distal row 
of the carpus. They are all arthrodial diarthroses, and the opposed articular 
surfaces present alternate elevations and depressions which form a series of 
interlocking joints. The joint-cavities between the carpal bones of the distal row, 
and also the more extensive intermetacarpal joint cavities, open into this arti- 
culation. 
This series of joints is invested by a common capsule which is weakest on its 
radial side, but is otherwise well defined. Its fibres arrange themselves in small 
slips, which pass obliquely in different directions, and vary in number for each 
metacarpal bone. Thus the oblique palmar ligaments (ligamenta carpo-metacarpea 
volaria, Fig. 215) usually consist of one slip for each metacarpal bone, but there 
may be two slips, and the third metacarpal bone frequently has three, of which 
one lies obliquely in front of the tendon of the flexor carpi radialis muscle. 
The oblique dorsal ligaments (ligamenta carpo-metacarpea dorsalia) are similar 
short bands, of greater strength and clearer definition, by which the index meta- 
earpal is bound to the trapezium and trapezoid; the middle metacarpal to the 
os magnum, and frequently to the trapezoid; the ring metacarpal to the os 
magnum and unciform, and the metacarpal of the minimus to the unciform. 
__ Interosseous ligaments, one or sometimes two in number, occur within the capsule. 
They are usually situated in relation to one or both of the contiguous margins of 
the bases of the third and fourth metacarpal bones, from which they extend upwards 
to adjacent margins of the os magnum and unciform. Occasionally they are 
sufficiently developed to divide the joint cavity into radial and ulnar sections. 
