. "The formation of the neural tube by coalescence of mesenchymal cells followed by their conversion to epithelial cells to form a solid cord that subsequently hollows out (cavitates) to create a hollow tube. Secondary neurulation is the typical mechanism of formation of the neural tube posterior to the posterior neuropore in mammals." . . . "secondary neural tube formation" . "medullary cord biosynthesis" . "medullary cord formation" . "neural rod formation" . "secondary neurulation" . . . .