Rhombomeres are such segments that make up the rhombencephalon or hindbrain. Rhombomeres determine the pattern of the following maturation of the rhombencephalon into its final parts. Initially there are three primary brain vesicles&colon; prosencephalon, mesencephalon, and rhombencephalon. The diencephalon, mesencephalon and rhombencephalon constitute the brain stem of the embryo. The prosencephalon (forebrain), mesencephalon (midbrain) and rhombencephalon (hindbrain), further differentiated in the various vertebrate groups. The caudal rhombencephalon has been generally considered as the initiation site for neural tube closure.