Etymology: Gk, chorde + enkephalos, brain
the portion of the central nervous system that develops in the early weeks of pregnancy from the neural tube and includes the prosencephalon, the mesencephalon, the rhombencephalon, and the spinal cord. The chordencephalon is segmented and divided into the alar and basal plates. The alar plate becomes the sensory portion of the gray substance of the spinal cord. The basal plate becomes the motor portion of the gray substance. chordencephalic, adj.