EXTENSOR CARPI RADIALIS LOXGIOR—BREVIOR 323 



obliquity of the tendon. This ol^hquity (Introduction, page 286) will, however, 

 adfl s])eed and range of movement, and at the same time it will assist in drawing 

 the articular surfaces of the ell)OAV together, and so give strength to the joint. 



If the forearm be fully supinated, the contraction of the brachio-radialis will 

 cause some pronation; and it is only when the forearm is in the position of full 

 pronation that it will produce a slight supination. It is therefore incorrect to 

 describe the muscle as a supinator. 



Relations. — In the up})er arm, it has at its inner side the brachialis antieus, 

 in which it forms a deep groove, and the musculo-spiral nerve and superior pro- 

 funda vessels. Outside and Ijehind lies the inner head of the triceps. Below, it 

 rests on the upper border of the extensor carpi radialis longior. In the forearm it 

 is covered, above by the deep fascia and superficial veins; below, by the extensor 

 ossis metacarpi and the extensor brevis pollicis. Beneath it lie the extensor 

 carpi radialis, longior, the supinator brevis, the pronator radii teres, the flexor 

 sublimis digitorum, the flexor longus pollicis, and the radial vessels and nerve. 



Variations. — The bracliio-radialis is sometimes absent. It may receive a slip from the 

 brachialis antieus. It may give slips to various parts of the radius, to the carpal bones on the 

 radial side of the hand, to the tendons of the extensor carpi radialis longior, the extensor ossis 

 metacarpi pollicis, the flexor longus pollicis, or to the supinator brevis muscle. 



2. EXTEXSOR CAEPI RADIALIS LOXGIOR 



The extensor carpi radialis longior — named from its action, position, and 

 length in comparison with its fellow extensor — is a narrow fusiform sheet. 



Origin. — (1) The lower third of the external cond3dar ridge; (2) the front of 

 the external intermuscular septum; (3) the front of the common tendon by which 

 the extensors at the back of the forearm arise from the external condyle. 



Insertion. — The back of the base of the second metacarpal bone near its radial 

 border. 



Structure. — Arising by fleshy fibres, this muscle has a somewhat penniform 

 arrangement. Its tendon is first seen" near the outer l)order on the deep surface of 

 the muscle, and becomes free at the junction of the middle and upper thirds of the 

 forearm. It lies upon and in close association with the tendon of the short 

 extensor, and passes through the second compartment in the posterior annular 

 ligament to its insertion upon the metacarpal bone. Its surfaces, like those of the 

 preceding muscle, are at first directed outwards and inAvards, and afterwards for- 

 wards and l)ackwards. 



Nerve-supply. — From the posterior cord of the brachial plexus (through the 

 sixth cervical nerve), by a branch from the mvisculo-spiral nerve which enters the 

 muscle at the upper part of its deep surface. 



Action. — (1) To extend the wrist; including under this appellation the carpo- 

 metacarpal, intercarpal, and radio-carpal joints. It is also a slight abductor of 

 these joints. "When the fingers have to be bent by the long flexors, it steadies the 

 carpus and metacarpus so as to limit the action of the flexors to the phalanges. 

 (2) It has also some influence in flexion of the elbow-joint. 



Relations. — In the arm, it lies between the brachialis antieus and the triceps, 

 and it is covered by the brachio-radialis. In the forearm, it overlies the short 

 radial extensor and wrist-joint, while it lies beneath the brachio-radialis and the 

 extensors of the thumb. 



Variations. — The extensor carpi radialis longior may be united with the brevier. It may give 

 tendinous slips to the bases of the first or third metacariml bones, or to the trapezium ; or a slip 

 may join the extensor ossis metacarpi pollicis, or some of the interossei. 



3. EXTEXSOR CARPI RADIALIS BREVIOR 



The extensor carpi radialis brevior — named for similar reasons to those which 

 give its name to the ])n'ceding muscU — is also flat and fusiform. 



Origin. — (1) The cimnnon tendon attached to the external condyle; (2) the 



