MUSCLES ON THE DOKSAL SUKFACE OF THE FOEEARM. 401 



Actions of the Muscles of the Forearm and Hand. 



These muscles are concerned 'in the movements of the elbow, wrist, and digits. 

 In the majority of cases the muscles act upon more than one joint. 



1. Action on the Elbow-Joint. It has been shown already that flexion and extension 

 of the elbow are assisted by certain of these muscles. The flexor muscles are the pronator 

 teres, and the flexor muscles of the wrist and fingers. In the position of pronation, the move- 

 ment of flexion is aided by the brachioradialis and extensor muscles of the wrist and fingers. 

 The extensors are the supinator muscle and anconaeus, and the extensor muscles of the wrist and 

 fingers. 



2. Pronation and supination of the hand are performed by special muscles, aided by muscles 

 which act also upon other joints. The brachioradialis assists in flexion and pronation on the one 

 hand, and in extension and supination on the other hand. In the supine position it assists 

 pronation, and in the prone position it assists supination, in each case bringing the hand into 

 the position intermediate between pronation and supination. 



3. Action on the Wrist- Joint. The movements at the wrist-joint are flexion and extension, 

 abduction and adduction. Flexion and adduction are much more extensive movements than 

 extension and abduction, on account of the form of the wrist-joint. The following muscles pro- 

 duce these movements : 



4. Movements of the Fingers. Two separate series of movements occur in relation to the 

 articulations of the fingers : flexion and extension (at the metacarpo-phalangeal and inter- 

 phalangeal joints), and abduction and adduction (only at the metacarpo-phalangeal joints). The 

 movements and the muscles concerned are given in the following tables : 



Flexion is more powerful and complete than extension of the fingers. The flexor digitorum 

 profundus alone acts on the terminal phalanges ; the flexor sublimis and flexor profundus together 

 flex the proximal inter-phalangeal joint ; and flexion of the metacarpo-phalangeal articulation is 

 effected by these muscles, assisted by the interossei, lumbricales, and flexor digiti quinti brevis. 

 Extension of the phalanges is effected by the united action of the extensors of the digits, the 

 interossei and lumbricales ; extension of the fingers at the metacarpo-phalangeal joints is produced 

 solely by the long extensor muscles. Separate extension of the index finger only is possible ; the 

 three inner fingers can only be flexed and extended together, on account of the connecting bands 

 joining the extensor tendons together on the back of the hand. 



5. Movements of the Thumb. The movements of which the thumb is capable are flexion 



27 



