presumptive hindbrain
The rhombencephalon (or hindbrain) is a developmental categorization of portions of the central nervous system in vertebrates. The rhombencephalon can be subdivided in a variable number of transversal swellings called rhombomeres. In the human embryo eight rhombomeres can be distinguished, from caudal to rostral: Rh7-Rh1 and the isthmus (the most rostral rhombomere). A rare disease of the rhombencephalon, 'rhombencephalosynapsis' is characterized by a missing vermis resulting in a fused cerebellum. Patients generally present with cerebellar ataxia. The caudal rhombencephalon has been generally considered as the initiation site for neural tube closure.