318 THE ARTICULATIONS, OR JOINTS 



IX. Carpometacarpal Articulations (Articulationes Carpometacarpeae) 



(Figs. 254, 255). 



1. ARTICULATION OF THE METACARPAL BONE OF THE THUMB WITH THE 

 TRAPEZIUM (ARTICULATIO CARPOMETACARPEA POLLICIS). 



This is a joint of reciprocal reception, and enjoys great freedom of movement, 

 on account of the configuration of its articular surfaces, which are saddle-shaped, 

 so that, on section, each bone appears to be received into a cavity in the other, 

 according to the direction in which they are cut. The joint is surrounded by a 

 capsular ligament. 



The capsular ligament is thick and fibrous, but loose, and passes from the cir- 

 cumference of the upper extremity of the metacarpal bones to the cough edge 

 bounding the articular surface of the trapezium; it is thickest externally and behind, 

 and lined with a separate synovial membrane. 



Movements. In the articulation of the metacarpal bone of the thumb with the trapezium, 

 the movements permitted are flexion, extension, adduction, abduction, and circumduction. When 

 the joint is flexed the metacarpal bone is brought in front of the palm and the thumb is gradu- 

 ally turned to the ringers. It is by this peculiar movement that the tip of the thumb is opposed 

 to the other digits; for by slightly flexing the fingers the palmar surface of the thumb can be 

 brought in contact with their palmar surfaces. 



2. ARTICULATIONS OF THE METACARPAL BONES OF THE FOUR INNER FINGERS 

 WITH THE CARPUS (ARTICUfcATIONES CARPOMETACARPEAE). 



The joints formed between the carpus and four inner metacarpal bones are 

 arthrodial joints. The ligaments are: 



Dorsal. Palmar. 



Interosseous. 



The dorsal ligaments (ligamenta carpometacarpea dorsalis), the strongest and 

 most distinct, connect the carpal and metacarpal bones on their dorsal surface. 

 The second metacarpal bone receives two fasciculi one from the trapezium, 

 the other from the trapezoid; the third metacarpal receives two one from the 

 trapezoid and one from the os magnum; the fourth, two one from the os magnum 

 and one from the unciform; the fifth receives a single fasciculus from the unciform 

 bone, which is continuous with a similar ligament on the palmar surface, thus 

 forming an incomplete capsule. 



The palmar ligaments (ligamenta carpometacarpea volaria) have a somewhat 

 similar arrangement on the palmar surface, with the exception of the third meta- 

 carpal, which has three ligaments an external one from the trapezium, situated 

 above the sheath of the tendon of the Flexor carpi radialis; a middle one, from 

 the os magnum; and an internal one, from the unciform. 



The interosseous ligaments consist of short, thick fibres, which are limited to 

 one part of the carpometacarpal articulation; they connect the contiguous inferior 

 angles of the os magnum and unciform with the adjacent surfaces of the third 

 and fourth metacarpal bones. 



Synovial Membrane. The synovial membrane is a continuation of that between the two 

 rows of carpal bones. Occasionally, the articulation of the unciform with the fourth and fifth 

 metacarpal bones has a separate synovial membrane. 



