The notochord or chorda dorsalis of the amphioxus, in which it is the only axial skeleton, and in fishes and amphibians, in which it is still persistent in the axial skeleton, is of entodermal origin, while in the higher vertebrates the notochordal process and the mesoderm are apparently derived from the ectoderm. In developing embryos of the higher vertebrates, it becomes enclosed in the centers of the vertebrae and in the modified vertebrae forming the base of the cranium, in which sites it eventually and usually early in the mammals, degenerates, with the exception of residuals known as pulpy masses or nuclei pulposi located in the intervertebral discs.
The normal embryonic residual notochord tissue is composed of rather large, round or slightly oval, acidophilic epithelial cells which develop vacuoles containing mucein. In later stages, the cell wall disappears, thus freeing the cytoplasm which fuses with that of other adjacent cells,
LEWIS NDC. A CONTRIBUTION TO THE STUDY OF TUMORS FROM THE PRIMITIVE NOTOCHORD. Arch Intern Med (Chic). 1921;28(4):434-452. doi:10.1001/archinte.1921.00100160069005