Homunculus

Homunculus--the "little man" once believed to inhabit the sperm cell, comprising the beginnings of a fetus. (Porter, Blood and Guts: A Short History of Medicine)

Alternatively, a homunculus is a "map of motor control...drawn on the cerebral cortex to show how the muscles are innervated from the cortex." (Weiss, Neurology for the Speech-Language Pathologist, p. 25)