LIGAMENTS OF THE WRIST AND METACARPUS. 



327 



between the neck of the os magnum and the scaphoid enlarges. In abduction (radial 

 fltxion) (Fig. 348, A) the second row of the carpus has a larger share in the motion 

 thdn in adduction. The meniscus moves to the ulnar side and is flexed, while its 

 ends approach each other, narrowing the arch. The lower end of the scaphoid is 

 crowded against the os magnum and the proximal end of the unciform recedes from 

 the semilunar. Lateral motions do not occur when the wrist is either strongly flexed 

 or extended. The screw surfaces of the cuneiform and unciform are important 

 factors in the combination of antero-posterior and lateral motions ; but the os mag- 

 num and unciform, which move together, do not twist in the socket formed by the 

 first row if the latter be fixed. Circumduction is a combination of the preceding 

 motions. Though the meniscus moves as a whole, the scaphoid is less closely 

 attached to the semilunar than is the cuneiform. 



Fig. 348. 



Reduced tracings from skiagraphs, showing the position of the carpal bones. A, in radial flexion ; B, in ulnar flexion.' 



Flexion is limited by the tension of the dorsal ligaments ; extension in the 

 upper joint chiefly by the lateral ligaments, in the lower by the locking of the bones 

 of the nfeniscus against those of the first row. The anterior fibres of the capsule 

 probably assist. Lateral motion is checked in the upper joint by the side liga- 

 ments ; in the lower joint it is limited chiefly by the shape of the bones. The 

 number of joints between the carpal bones divide the force of shocks transmitted 

 through the hand. 



The motions of the carpo-metacarpal joints of the fingers are almost wanting, 

 except for the ring and little fingers. In both these the motion is essentially flexion, 

 most marked in the latter, and, owing to the dorsal convexity of the carpus, tending 

 to oppose the little finger to the thumb. 



The metacarpo-phalangeal articulations are surrounded by a rather loose 

 caps2de, which is inserted into both bones pretty close to the articular cartilage. 

 It is weakest on the dorsum, where it is supported by the extensor tendons. It 



' In tracings from X-ray photographs it is in places very difficult satisfactorily to outline the 

 separate bones, partly because the contours of both surfaces as well as of thick processes are 

 shown, and partly because some bones lie in front of others, owing to the palmar concavity of 

 the wrist. .The greatest difficulty is with the respective outlines of the trapezium and trapezoid. 

 In the above figures the outline of the latter is indicated in dotted fines. This confusion is of 

 little practical importance, since the drawings are to illustrate the changes of position between 

 the first row and the forearm on one side and the second row on the other. 



