Which of the following tendons passes below the sustentaculum Tali ?

The attachments and relations of the medial surface of calcaneum as follows - The groove on the lower surface of the sustentaculum tali is occupied by the tendon of the flexor hallucis longus. The medial margin of the sustentaculum tali is related to the tendon of the flexor digitorum longus and provides attachment to: (a) the spring ligament anteriorly. (b) a slip from the tibialis posterior in the middle; (c) some of the superficial fibres of the deltoid ligament along the whole length; and (d) the medial talocalcanean ligament posteriorly. Below the groove for the flexor hallucis longus, the medial surface gives origin to the fleshy fibres of the medial head of the flexor digitorum accessorius. B D Chaurasia's Human Anatomy , seventh edition , volume 2 , pg. no.,36.