interossei & lumbricals

• Dorsal Interossei: Four bipennate muscles

  O: Sides of adjacent metacarpals

  R: Distally

  I: DDEs and bases proximal phalanges of digits 2 – 4

  A: Abduction and flexion of MCPs of digits 2-4 and extension of IPs (through DDE)

  NS: Deep branch ulnar nerve (C(7),8,T1)
• Palmar Interossei: Four unipennate muscles

  O: Palmar surfaces 1st (often rudimentary), 2nd, 4th and 5th MC shafts

  R: Distally

  I: DDEs and bases proximal phalanges of digits (1), 2, 4 and 5

  A: Adduction and flexion of MCPs and extension of IPs (through DDE)

  NS: Deep branch ulnar nerve (C(7), 8 and T1)
• Lumbricals: Four small muscles in palm of hand (associated with tendons of flexor digitorum profundus)

  Lateral two (unipennate)

  O: Lateral side of lateral FDP tendons on digits 2 and 3

  I: Lateral edge DDEs at base of proximal phalanx
• Lumbricals:

  Medial two (bipennate)

  O: Adjacent sides FDP tendons on digits 3, 4 and 5

  I: Lateral edge DDEs at base of proximal phalanx

  A: Flexion MCPs and extension IPs

  NS: Lateral 2: Median nerve (C5-8,T1)

  Medial 2: Deep branch ulnar nerve (C(7),8,T1)