In vertebrates, the development of the CNS starts with the formation of the neural plate on the dorsal surface of the embryo during late gastrulation [213, 214]. A complex morphogenetic process transforms the neural plate into the hollow neural tube in a process known as “neurulation” . Primary neurulation is responsible for formation of the neural tube throughout the brain and the spinal cord rostral to the mid-sacral level . At more caudal levels, an alternative mechanism (secondary neurulation) operates whereby the neural tube is formed by canalization of a condensed rod of mesenchymal cells in the tail bud .