Medial boundary of the anatomical snuff box is formed by:

Ans. A. Extensor pollicis LongusThe anatomical snuff box or snuffbox is a triangular deepening on the radial, dorsal aspect of the hand--at the level of the carpal bones, specifically, the scaphoid and trapezium bones forming the floor. The name originates from the use of this surface for placing and then sniffing powdered tobacco, or "snuff."Boundariesa. The medial border (ulnar side) of the snuffbox is the tendon of the extensor pollicis longus.b. The lateral border (radial side) is a pair of parallel and intimate tendons, of the extensor pollicis brevis and the abductor pollicis longus