In terms of development, the human central nervous system is often classified based on the original three primitive vesicles from which it develops: These primary vesicles form in the normal development of the neural tube of the embryo and initially include the prosencephalon, mesencephalon, and rhombencephalon, in rostral to caudal (from head to tail) orientation. Later in development of the nervous system each section itself turns into smaller components. During development, the cells that migrate tangentially to form the basal ganglia are directed by the lateral and medial ganglionic eminences. The following table demonstrates this developmental classification and traces it to the anatomic structures found in the basal ganglia. The structures relevant to the basal ganglia are shown in bold.