Flexor retinaculum is a strong fibrous band which bridges the anterior concavity of the carpal bones thus converts it into a tunnel, the carpal tunnel.
These four bony points are all palpable in the living hand and it should be noted that pisiform is the only carpal bone that gives attachments to both flexor and extensor retinacula.
On either side the retinaculum has a slip.
- Lateral deep slip - It is attached to the medial lip of the groove on the trapezium thus converts it into a fibro-osseous tunnel that transmits the tendon of the flexor carpi radialis and its synovial sheath.
- Medial superficial slip - It is attached to the pisiform bone and it forms a small canal (of Guyon). The ulnar vessels and nerves pass deep to this slip. Occasionally Compression of the ulnar nerve may occur within this canal.  
Principal function of the flexor retinaculum is to serve as a pulley for the carpal flexor muscles and to stabilize the carpal system .
- The volar surface gives rise to muscles of the thenar and hypothenar eminences
- It is Related to the tendon of the palmaris longus
- Its Upper margin continues in the palmar carpal ligament and lower margin merges with the palmar aponeurosis
- Chaurasia BD. BD Chaurasia's Human Anatomy. CBS Publishers & Distributors PVt Ltd.; 2010. p112-13.
- Sinnatamby CS. Last's Anatomy, International Edition: Regional and Applied. Elsevier Health Sciences; 2011 Apr 19.
- Dr.Prakash GB. The flexor retinaculum of Hand : Gross anatomy, attachments and relations. Available from:https://www.youtube.com/watch?v=J47tdKW3ibg&feature=youtu.be(Last accessed 09/10/2020)
- Deak N, Bordoni B. Anatomy, Shoulder and Upper Limb, Wrist Flexor Retinaculum.(accessed 09 October, 2020)