ectoderm-derived structure primary nerve cord https://github.com/obophenotype/uberon/issues/691 A cluster of neurons that is the most prominent longitudinally extending condensed part of a nervous system. some species have multiple longitudinal nerve cords; this class refers to the most prominent one, which is dorsal in chordates and ventral in others. nerve cord BILA:0000136 true nerve cord BTO:0001656 UBERON:0005053 multicellular anatomical structure