The palmar interossei muscles are a group of four muscles located between the metacarpal bones. Relative to the dorsal interossei, they reside in a more superficial layer relative to the palmar surface.
The palmar interossei arise from the ulnar side of the 1st and 2nd metacarpals and the radial side of the 4th and 5th metacarpals. Each muscle independently inserts into the base of the proximal phalanx and extensor expansion of the same digit. The exception is the first palmar interosseous which inserts into the ulnar sesamoid bone of the thumb.
Their functions are varied:
- adduction of the fingers to the midline of the hand
- flexion of the metacarpophalangeal joints
- extension of the interphalangeal joints
They are innervated by the deep branch of the ulnar nerve (C8, T1).