[Neurosurgical embryology. Part 7: Development of the spinal cord, the spine and the posterior fossa].

The spinal cord arises from the most caudal domain of the neural tube whereas the vertebrae develop from the para-axial mesoderm (namely the somites). The development of the spinal cord and the vertebrae is so intimately linked that it is more convenient to present it in the same chapter. The neural tube is formed from the neural plate during neurulation. This tube is submitted to a double gradient of diffusible molecules that lead to the ventro-dorsal polarization of the tube. This polarization is figured as the emergence of sub-domains that contain progenitors engaged in a specific lineage. Axial organs induce the dissociation of the somites, giving rise to the dermatome, myotome and sclerotome. Vertebrae derive from the sclerotome after the so-called resegmentation of the somites. During this process, a caudal hemi-somite is associated with the rostral hemi-somite of the next caudal somite to differentiate into the vertebra. The occipital bone forms the major part of the walls of the posterior fossa. This bone develops from the para-axial mesoderm for its sub-tentorial part whereas its sus-tentorial derives from neural crest cells.