Four or five such annular pulleys, together with three cruciate pulleys, form a fibro-osseous tunnel on the palmar aspect of the hand through which passes the deep and superficial flexor tendons.

The annular and cruciate ligaments serve to govern the flexor mechanism of the hand and wrist, providing critical constraints to the flexor tendons to prevent bowstringing upon contraction and excursion of extrinsic flexor musculo-tendinous units.

[1] The first annular pulley (A1 pulley), near the head of the metacarpal bone, lies in the flexor groove in the deep transverse metacarpal ligament.

As a general rule, the A1, A3, and A5 pulleys in the fingers are "joint pulleys" that originate from the volar plate on the volar aspect of the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints, respectively.

[1] The first annular pulley (A1 pulley), near the head of the metacarpal bone, lies in the flexor groove in the deep transverse metacarpal ligament.