Interossei muscles (dorsal hand, anatomy)

The dorsal interossei muscles are a group of four muscles located between the metacarpal bones. Relative to the palmar interossei, they reside in a deeper plane nearer to the dorsal surface of the hand and they tend to be larger.

The dorsal interossei arise from the apposing sides of neighbouring metacarpal shafts. Each muscle independently inserts into the base of the proximal phalanx and extensor expansion of the second to fourth digits:

• first dorsal interosseous into radial side of index finger
• second dorsal interosseous into radial side of middle finger
• third dorsal interosseous into ulnar side of middle finger
• fourth dorsal interosseous into ulnar side of ring finger

Their functions are varied:

• abduction of the fingers from 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).