3^6 A MANUAL OF ANATOMY 



(2) the inner half of the front of the interosseous membrane ; (3) the 

 upper two-thirds of the inner surface of the ulna ; and (4) the 

 posterior border of the bone for a similar extent, by an aponeurosis 

 common to it, the flexor carpi ulnaris, and extensor carpi ulnaris. 



Insertion. — ^The front of the bases of the distal phalanges of 

 the four inner fingers. 



The tendinous part of the muscle makes its appearance about 

 the centre of the forearm, and the index-finger tendon is usually 

 separate from the rest of the tendinous mass over the greater part 

 of its extent. The other three tendons become separate beneath 

 the anterior annular ligament, so that in the palm there are four 

 diverging tendons, connected with which are the lumbricales. Each 

 deep flexor tendon accompanies a superficial flexor tendon, beneath 

 which it lies, and both enter the sheath on the palmar aspect of a 

 finger. Opposite the distal end of the first phalanx the deep tendon 

 passes through the cleft in the superficial tendon, and so reaches its 

 more distant point of insertion. 



Nerve- supply. — (i) The anterior interosseous branch of the 

 median supplies that portion of the muscle which acts upon 

 the index finger, and in part the portion acting upon the middle 

 and ring fingers ; and (2) the ulnar nerve supplies that portion 

 which acts upon the little finger, and in part the portion acting 

 upon the ring and middle fingers. Sometimes the anterior 

 interosseous nerve supplies the whole of the portion acting upon 

 the middle finger. 



Action. — (i) To flex the distal phalanges of the four inner fingers ; 

 (2) to assist in flexing the second phalanx and metacarpo-phalangeal 

 joint ; and (3) to assist in flexing the wrist-joint. 



2. Flexor Longus PoUicis — Origin. — (i) The anterior surface of 

 the radius, from the anterior oblique line above to the upper border 

 of the pronator quadratus below ; (2) the outer half of the front 

 of the interosseous membrane ; and (3) as a rule by a tendinous 

 slip from the inner margin of the coronoid process of the ulna, or 

 from the internal epicondyle of the humerus. 



Insertion. — The front of the base of the distal phalanx of the thumb. 



The tendon appears on the front of the muscle about the centre 

 of the forearm, and receives fleshy fibres until it is near the wrist. 



Nerve-supply. — ^The anterior interosseous nerve. 



Action. — (i) To flex the distal phalanx of the thumb ; (2) to 

 assist in flexing its metacarpo-phalangeal joint ; and (3) to act as 

 an auxiliary flexor of the wrist-joint. 



3. Pronator Quadratus — Origin. — ^The front of the ulna over its 

 lower fourth. 



Insertion. — The front of the radius for about 2 inches at its 

 lower end, and the anterior part of the inner surface. 



Nerve-supply. — ^The anterior interosseous nerve. 



The fibres are disposed, for the most part, transversely, and the 

 muscle is covered by a firm aponeurosis over about its inner third. 



Action. — To pronate the radius upon the ulna. 



