tendinous sheath of flexor pollicis longus (radial bursa)

The palmar carpal synovial tendon sheath that envelopes the flexor pollicis longus in its course through the carpal canal; it is continuous with the digital sheath of the thumb, the two generally being considered as one sheath.

References

Stedman's Medical Dictionary 27th ed, Williams & Wilkins, Baltimore, 1999.