Introduction The muscles of the hand can be divided into extrinsic and intrinsic muscles extrinsic hand muscles these are muscles that are located outside of the hand (thus extrinsic) they are located in the forearm extrinsic extensor muscles of the hand are located in the posterior compartment of the forearm extrinsic flexor muscles of the hand are located in the anterior compartment of the forearm intrinsic hand muscles these are muscles that are located inside the hand (thus intrinsic) these include the thenar muscles hypothenar muscles interosseous muscles lumbricals Thenar Muscles Introduction the thenar muscles form the thenar eminence on the lateral surface of the palm the thenar hand muscles include Opponens pollicis Abductor pollicis brevis Flexor pollicis brevis mnemonic: "OAF" these muscles are innervated by the median nerve and are involved in fine movements of the thumb Function the thenar hand muscles are involved in Opposition Abduction Flexion mnemonic: "OAF" Hypothenar Muscles Introduction the hypothenar muscles form the hypothenar eminence on the medial surface of the palm the hypothenar muscles include Opponens digiti minimi Abductor digiti minimi Flexor digiti minimi mnemonic: "OAF" these muscles are innervated by the ulnar nerve Function the hypothenar muscles are involved in Opposition Abduction Flexion mnemonic: "OAF" Interossei and Lumbricals Introduction interossei can be divided into dorsal and palmar interossei function dorsal interossei abduction of the fingers at the metacarpophalangeal (MCP) joint palmar interossei adduction of the fingers at the MCP joint mnemonic "DAB" = Dorsals ABduct "PAD" = Palmars ADduct innervation the dorsal and palmar interossei are innervated by the ulnar nerve lumbricals there are 4 lumbrical muscles of the hand they attach to the flexor digitorum profundus tendon proximally tendons of the extensor expansion distally function flexion of the MCP joint extension the interphalangeal (IP) joints innervation the median nerve innervates the lateral lumbricals (the 1st and 2nd lumbrical) the ulnar nerve innervates the medial lumbricals (the 3rd and 4th lumbrical)