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Noun, pl. notochords

1. A flexible rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes the nucleus pulposus of the intervertebral disc. The notochord is found ventral to the neural tube. (

2. A flexible rodlike structure that forms the main support of the body in the lowest chordates; a primitive spine. (

3. A similar structure found in the embryos of vertebrates from which the spine develops. (

4. A longitudinal flexible rod of cells that in the lowest chordates (as a lancelet or a lamprey) and in the embryos of the higher vertebrates forms the supporting axis of the body. (

Word origin: coined in English by English anatomist Sir Richard Owen (1804-1892) from chord, alteration of cord (n.), by influence of Greek khorde “gut-string, string of a lyre, tripe,” + comb. form of Greek noton “back,”

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