The two tendons concerned are the tendons of the extensor pollicis brevis and abductor pollicis longus muscles.

On the palmar (lateral) side of the base is the insertion of the tendon of the abductor pollicis longus muscle, usually featuring a small tubercle.

Abductor pollicis longus muscle (musculus abductor pollicis longus)

Its lower part is narrow, and covered by the tendons of the abductor pollicis longus muscle and extensor pollicis brevis muscle.

The lateral surface of this process is marked by a flat groove, for the tendons of the abductor pollicis longus muscle and extensor pollicis brevis muscle.

The abductor pollicis longus muscle is innervated by the posterior interosseous nerve, which is a continuation of the deep branch of the radial nerve after it passes through the supinator muscle.