360 



THE ARTICULATIONS. 



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

 behind, and lined by 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 gradually turned to the fingers. It is bv this 

 peculiar movement that the tip of the thumb is opposed to the other digits ; for 

 by slightly flexing the fingei'S the palmar surface of the thumb can be brought in 

 contact with their palmar surfaces one after another. 



2. ARTICULATIONS or THE METACARPAL BONES OF THE FOUR INNER 

 FINGERS WITH THE CARPUS. 



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

 arthrodial joints. The ligaments are 



Dorsal. 



Palmar. 



Interosseous. 



The Dorsal Ligaments, 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, forming an 

 incomplete capsule. 



The Palmar Ligaments have a 

 somewhat similar arrangement on the 

 palmar surface, with the exception 

 of the third metacarpal, 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 inter- 

 nal one, from the unciform. 



The Interosseous Ligaments con- 

 sist of short, thick fibres, Avhich are 

 limited to one part of the earpo- 

 metacarpal articulation ; they con- 

 nect the contiguous inferior angles 

 of the os magnum and unciform with 

 the adjacent surfaces of the third 

 and fourth metacarpal bones. 



The Synovial Membrane is a con- 

 tinuation 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. 



The synovial membranes of the wrist and carpus (Fig. 251) are thus seen to 

 be five in number. The first, the membrana sacciformis, passes from the lower 

 end of the ulna to the sigmoid cavity of the radius, and lines the upper surface 

 of the interarticular fibro-cartilage. The second passes from the lower end of 

 the radius and interarticular fibro-cartilage above to the bones of the first row- 

 below. The third, the most extensive, passes between the contiguous margins of 

 the two rows of carpal bones between the bones of the second row to the carpal 



FIG. 251. Vertical section through the articulations at 

 the wrist, showing the five synovial membranes. 



