part of develops from ends during starts during brain midbrain-hindbrain boundary The part of the brain that is the morphological boundary between the midbrain and hindbrain and that is the location of an organizing center which patterns the midbrain and hindbrain primordia of the neural plate. isthmic organizer territory UBERON:0003052 XAO:0000016 xenopus_anatomy isthmus MHB neural plate death anatomical line presumptive midbrain-hindbrain boundary NF stage 22