Evidence that the caudal portion of the neural tube develops by cavitation of a neural cord in the caudal eminence of human embryos.

The formation of the secondary neural tube was traced in serial sections of human embryos of developmental stages 13 to 17 (32-41 days after fertilisation). It was found that the secondary neural tube formation begins with cavitation of the neural cord. The minute cavities are seen in embryos at stages 13 and 15. At stages 16 and 17 the numerous cavities coalesce to form a single central canal.