400 THE MUSCLES AND FASCIAE. 



radialis longior by the sixth and seventh, and the Anconeus by the seventh and 

 eighth cervical nerves, all through the musculo-spiral nerve ; the remaining muscles 

 of the radial and posterior brachial region are supplied through the posterior 

 interosseous nerve, the Supinator brevis being supplied by the sixth cervical, the 

 Extensor carpi radialis brevior by the sixth and seventh cervical, and all the other 

 muscles by the seventh cervical. 



Actions. The muscles of the radial and posterior brachial regions, which 

 comprise all the extensor and supinator muscles, act upon the forearm, wrist, and 

 hand ; they are the direct antagonists of the pronator and flexor muscles. The 

 Anconeus assists the Triceps in extending the forearm. The chief action of the 

 Supinator longus is that of a flexor of the elbow-joint, but in addition to this it 

 may act both as a supinator or a pronator ; that is to say, if the forearm is forcibly 

 pronated it will act as a supinator, and bring the bones into a position midway 

 between supination and pronation ; and, vice versd, if the arm is forcibly supinated, 

 it will act as a pronator, and bring the bones into the same position, midway 

 between supination and pronation. The action of the muscle is therefore to throw 

 the forearm and hand into the position they naturally occupy when placed across 

 the chest. The Supinator brevis is a supinator ; that is to say, when the radius 

 has been carried across the ulna in pronation and the back of the hand is directed 

 forward, this muscle carries the radius back again to its normal position on the 

 outer side of the ulna, and the palm of the hand is again directed forward. The 

 Extensor carpi radialis longior extends the wrist and abducts the hand. It may 

 also assist in bending the elbow-joint; at all events, it serves to fix or steady this 

 articulation. The Extensor carpi radialis brevior assists the Extensor carpi radi- 

 alis longior in extending the wrist, and may also act slightly as an abductor of the 

 hand. The Extensor carpi ulnaris helps to extend the hand, but when acting 

 alone inclines it toward the ulnar side ; by its continued action it extends the 

 elbow-joint. The Extensor communis digitorum extends the phalanges, then the 

 wrist, and finally the elbow. It acts principally on the proximal phalanges, the 

 middle and terminal phalanges being extended by the Interossei and Lumbri- 

 cales. It has also a tendency to separate the fingers as it extends them. The 

 Extensor minimi digiti extends similarly the little finger, and by its continued 

 action it assists in extending the wrist. It is owing to this muscle that the little 

 finger can be extended or pointed whilst the others are flexed. The chief action of 

 the Extensor ossis metacarpi pollicis is to carry the thumb outward and backward 

 from the palm of the hand, and hence it has been called the abductor pollicis lon- 

 gm. By its continued action it helps to extend and abduct the wrist. The 

 Extensor brevis pollicis extends, the proximal phalanx of the thumb. By its 

 continued action it helps to extend and abduct the wrist. The Extensor longus 

 pollicis extends the terminal phalanx of the thumb. By its continued action it 

 helps to extend and abduct the wrist. The Extensor indicis extends the index 

 finger, and by its continued action assists in extending the wrist. It is owing 

 to this muscle that the index finger can be extended or pointed while the others 

 are flexed. 



Surgical Anatomy. The tendons of the Extensor muscles of the thumb are liable to 

 become strained and their sheaths inflamed after excessive exercise, producing a sausage-shaped 

 swelling along the course of the tendon, and giving a peculiar creaking sensation to the finger 

 when the muscle acts. In consequence of its often being caused by such movements as wringing 

 clothes, it is known as washerwoman's sprain." 



IV. MUSCLES AND FASCLE OF THE HAND. 



The Muscles of the Hand are subdivided into three groups : 1. Those of the 

 thumb, which occupy the radial side and produce the thenar eminence ; 2. Those 

 )t the little finger, which occupy the ulnar side and give rise to the hypothenar 

 eminence; 3. Those in the middle of the palm and within the interosseous 

 spaces. 



