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notochord no·to·chord (nō'tə-kôrd')
A flexible rodlike structure that forms the main support of the body in the lowest chordates; a primitive backbone.
A similar structure in embryos of higher vertebrates, from which the spinal column develops.
A flexible rodlike structure that forms the main support of the body in all chordates during some stage of their development. In vertebrates, the notochord develops into a true backbone in the embryonic phase. Primitive chordates, such as lancelets and tunicates, retain a notochord throughout their lives.
flexible rodlike structure of mesodermal cells that is the principal longitudinal structural element of chordates and of the early embryo of vertebrates, in both of which it plays an organizational role in nervous system development. In later vertebrate development, it becomes part of the vertebral column. The notochord derives during gastrulation (infolding of the blastula, or early embryo) from cells that migrate anteriorly in the midline between the hypoblast and the epiblast (inner and outer layers of the blastula). These cells coalesce immediately beneath the developing central nervous system. With the formation of the vertebral column, the notochord is incorporated into the column as the centres of the intervertebral discs, called the nuclei pulposi, which cushion the vertebrae.