ARTICULATIONS 165 



movements of abduction and adduction, it should be noticed that in the 

 extended position of the fingers they are very free ; but if flexion be 

 induced, the power of separating the fingers becomes more and more 

 restricted, until it becomes absolutely lost when the hand is closed. An 

 examination of the collateral ligaments will afford the explanation of this. 

 These "are attached so far dorsally on the metacarpal bones, as to be 

 much nearer to their distal ends than to their volar aspects " (Cleland). 

 Consequently, while they are comparatively lax in the extended position of 

 the fingers, the further flexion advances the tighter they become, and in 

 this way they interfere with the lateral movements of the first phalanges. 



The first phalanx of the thumb has only a limited range of movement 

 at the metacarpo-phalangeal joint. 



ARTICULATIONES DIGITORUM (JOINTS OF THE FINGERS). 



The ligaments connecting the phalanges are arranged upon 

 a plan identical with that already described in connection 

 with the metacarpo-phalangeal joints. This should not be 

 made an excuse, however, to slur them over. 



Movements. From the manner in which the articular surfaces are 

 adapted to each other, flexion and extension are the only movements which 

 can take place at the interphalangeal joints. Flexion of the second 

 phalanges of the fingers is brought about by the flexor sublimis, and of 

 the ungual phalanges by the flexor profundus. Extension of the phalanges 

 at the interphalangeal joints is largely produced by the interosseous and 

 lumbrical muscles acting through the extensor tendons, into which they are 

 inserted. These muscles, therefore, whilst they flex the first phalanx at 

 the metacarpo-phalangeal joints, extend the second and ungual phalanges 

 at the interphalangeal joints. 



In the case of the thumb, the long flexor and the extensor pollicis 

 longus operate at the interphalangeal joint. 



r 11 6 



