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The document discusses the development of the nervous system. It describes how in the third week the dorsal primitive line forms and the neural tube, notochord (cartilage skeleton), and crista neuralis develop. The neural plate, groove, and tube form between days 15-21. The neural crest cells separate from the neural tube and migrate throughout the embryo. The neural tube differentiates into the anterior two-thirds encephalon and posterior one-third medulla spinalis. The cranial and caudal neuropores close on days 25 and 27-28 respectively. Precisely defined nerve pathways develop in the limbs.Read less