CARPO-METACARPAL JOINTS. 



299 



the one row of bones may be separated far enough from the other, to allow 

 a sight of the articular surfaces. 



Articular surfaces. The first row of carpal bones (except pisiform) 

 forms internally an arch with the scaphoid (), semilunar (d), and cunei- 

 form bone (c), whose hollow is turned towards the second ; and externally 

 a prominence with the scaphoid (a) which is received into a concavity in 

 the other row. In the second row the os magnum (g) and os unciforme 

 (k) present a condyloid projection, which is received into the arch before 

 mentioned; but the two outer bones (trapezium and trapezoid, e and/) 

 are much below the level of the others, and form a slight hollow for the 

 reception of the outer part of the scaphoid bone. 



One synovial membrane serves for the articulation of all the carpal 

 bones, except the pisiform with the cuneiform. Lining the joint between 

 the two rows of the carpus, the membrane sends upwards and downwards 

 prolongations between the individual bones. The offsets upwards are two, 

 and they sometimes join the synovial membrane of the wrist joint ; but 

 the offsets in the opposite direction are three, and may be continued to all, 

 or only to some of the articulations between the four inner metacarpal with 

 their carpal bones. 



Movements. The transverse carpal joint is partly condyloid, but only 

 forward and backward motion is permitted. All lateral and circumduc- 

 tory movement is arrested, if the rows are closely applied together, by the 

 scaphoid striking against the os magnum on the one side, and the cunei- 

 form against the unciform on the other. 



Flexion. As the hand is bent forwards the lower row of carpal bones 

 moves backwards, and renders pro- 

 minent the posterior ligament. This 

 motion is also brought into play in 

 full bending of the wrist. 



Extension. The backward move- 

 ment is freer than flexion. As the 

 lower carpal row moves towards the 

 palm, its progress is checked by the 

 anterior ligament of the joint, and by 

 the strong flexor tendons. 



UNION OF THE METACARPAL 

 BONES. The metacarpal bones of 

 the four fingers are connected at 

 their bases by the following liga- 

 ment : A superficial dorsal (fig. 95) 

 and palmar fasciculus of fibres passes 

 transversely from one bone to the 

 next ; and the bands in the palm are 

 the strongest (fig. 92). Besides, 

 there is a short interosseous ligament 

 between the contiguous rough sur- 

 faces of the bones. 



Lateral union. Where the meta- 

 carpal bones touch they are covered 

 by cartilage ; and the articular sur- 

 faces are furnished with prolongations of the synovial membrane serving 

 for their articulation with the carpus. 



At the anterior extremities the same four metacarpal bones are con- 



Fig. 95. 



POSTERIOR LIGAMENTS OF THE WKI>T, AND 

 CARPAL AND METACARPAL BONES (Bour- 

 gery and Jacob). 



1. Posterior radio-carpal. 



2. Carpo-inetacarpal joint of the thumb. 



3. 3. Transverse bands between the bases of 



the metacarpal bones. 



