390 



THE MUSCULATURE 



Structure and insertion. — The fibre-bundles converge obliquely toward a tendon which 

 appears high up on the dorso-lateral surface of the muscle. Toward the lower third of the 

 forearm this tendon becomes a free, strong band closely apphed to the under surface of the 

 tendon of the long radial extensor, and with this passes through the second compartment be- 

 neath the dorsal ligament of the carpus, diverging as it does so toward its insertion into the 

 back of the bases of the second and third metacarpal bones. 



Fig. 368. — Tendons upon the Dorsum of the Hand. 



Abductor pollicis longus 

 Extensor pollicis brevis 



Dorsal carpal ligament 



Extensor carpi 

 radialis brevis 

 Extensor carpi 

 radialis longus 



Extensor pollicis 

 longus 



First dorsal 

 interosseous 



Adductor 

 pollicis 



— Extensor carpi ulnans 



Extensor digitorum communis 



Extensor digiti quinti 



- Extensor indicis proprius 



Attachment of extensor 

 digitorum communis 

 to second phalanx 



Attachment of extensor 

 digitorum communis 

 to third phalanx 



Nerve-supply. — A branch is supplied to the muscle from the deep radial (posterior interos- 

 seous) nerve before this enters the supinator (l)rcvis). The branch enters the middle third of 

 the medial margin of the muscle by several rami. The nerve fibres arise from the (fifth), 

 sixth and seventh cervical nerves. 



Adinn.— To extend the hand and, to a slight extent, to flex the forearm. 



Relations. — In its proximal portion the muscle is placed with a medial surface toward 

 the common extensor, a deep toward the supinator (brevis) and pronator teres, and a dorso- 

 lateral toward the long radial extensor. More distally the muscle and its tendon become 

 flattened al)out the radius and partly covered by the long radial extensor and its tendon. 



