muscles fully contained (origin, belly, and insertion) within the hand (palm and fingers); the intrinsic hand muscles are arranged in layers that are divided into radial (thenar), central (palmar), and ulnar (hypothenar) muscles; they act on the carpometacarpal, metacarpophalangeal, and interphalangeal joints directly or via the extensor apparati; most thenar intrinsic muscles are innervated by the median nerve; all other intrinsic hand muscles are innervated by the ulnar nerve.
