The lumbricals are four, small, worm-like muscles on each hand. These muscles are unusual in that they do not attach to bone. Instead, they attach proximally to the radial side of the tendons of
flexor digitorum profundus, and distally to the
extensor expansions.
Nerve supply The first and second lumbricals (the most radial two) are
innervated by the
median nerve. The third and fourth lumbricals (most ulnar two) are innervated by the deep branch of
ulnar nerve. This is the usual innervation of the lumbricals (occurring in 60% of individuals). However 1:3 (median:ulnar - 20% of individuals) and 3:1 (median:ulnar - 20% of individuals) also exist. The lumbrical innervation always follows the innervation pattern of the associated muscle unit of
flexor digitorum profundus (i.e. if the muscle units supplying the
tendon to the
middle finger are innervated by the median nerve, the second lumbrical will also be innervated by the median nerve).
Blood supply Four separate sources supply blood to these muscles: the
superficial palmar arch, the
common palmar digital artery, the
deep palmar arch, and the
dorsal digital artery. == Function ==