332 THE ARTICULATIONS OK JOINTS. 



ARTICULATIONES INTERMETACARPEJE. 



Intermetacarpal Joints. The four medial 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-rnetacarpal joint (not yet described), and hence the ligamentous 

 arrangements only enclose three aspects of each joint. 



Three strong transverse ligaments (Figs. 310 and 311) bind adjacent volar, 

 dorsal, and interosseous areas of the bases of the metacarpal bones, and hence they 

 are called ligamenta basium (oss. rnetacarp.) volaria, dorsalia et interossea. A 

 synovial stratum is associated with each of these joints, but it may be regarded as 

 a prolongation from the carpo-metacarpal articulation. 



ARTICULATIONES CARPOMETACARPEA;. 



Carpo-metacarpal Joints. The articulation of the metacarpal bone of the 

 thumb with the greater multangular differs in so many respects from the articula- 

 tion between the other metacarpal bones and the carpus, that it must be considered 

 separately. 



(A) The articulatio carpometacarpea pollicis (Figs. 310 and 311) is the joint 

 between the disto-lateral surface of the greater multangular and the proximal 

 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 an articular capsule, in the fibrous stratum of 

 which we may recognise volar, dorsal, lateral, and medial bands, the last being 

 the strongest and most important. 



A synovial stratum lines the fibrous stratum, and the joint cavity is isolated 

 and quite separate from the other carpal and carpo-metacarpal articulations. 



At tliis joint movements occur around 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 circumduction may be produced. 



(E) The articulationes carpometacarpeae digitorum are the joints between 

 the bases of the four medial 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 articulation. 



This series of joints is invested by a common articular 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 ligamenta carpometacarpea volaria (volar carpo- 

 metacarpal ligaments (O.T. oblique palmar)) (Fig. 310) 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 ligamenta carpometacarpea dorsalia (dorsal carpo-metacarpal ligaments (O.T. 

 oblique dorsal)) are similar short bands, of greater strength and clearer definition, 

 by which the index metacarpal is bound to the greater and lesser multangular 

 bones ; the middle metacarpal to the capitate, and frequently to the lesser mult- 

 angular ; the ring metacarpal to the capitate and os hamatum, and the metacarpal 

 of the 5th finger to the os hamatum. 



Ligamenta interossea (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 proximally to adjacent margins of the capitate and os hamatum. 

 Occasionally they are sufficiently developed to divide the joint cavity into radial 

 and ulnar sections. 



