The notochord is 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 lower vertebrates, it persists throughout life as the main axial support of the body, while in higher vertebrates it's replaced by the vertebral column. The notochord is found on the ventral surface of the neural tube. Notochords were the first "backbones", as well, serving as support structures in chordates that lack… (More on Notochord)