A, Anteroposterior radiograph of dissected right hand. Wires mark proximal and distal extents of classic flexor retinaculum, which includes middle portion of flexor retinaculum (transverse carpal ligament) and distal portion of flexor retinaculum. Note proximal limit is at distal aspect of pisiform (P) and distal limit is distal to hook of hamate (H). B, Three portions of flexor retinaculum (1 to 3) consist of thick aponeurosis between thenar (A) and hypothenar (B) muscles. Thenar muscles attach to radial half of classic flexor retinaculum, composed of distal portion of flexor retinaculum (3); trapezial ridge (T) and scaphoid tubercle (S) also are shown. Proximal portion of flexor retinaculum (1) courses deep to flexor carpi ulnaris (U) and flexor carpi radialis ®. Flexor carpi radialis tendon is shown as it pierces flexor retinaculum at junction of proximal and middle portions to enter its fibroosseous canal. F, Antebrachial fascia; M, third metacarpal.