Dorsoventral patterning in the neural development of vertebrates is controlled by the induction and polarizing properties of the floor plate . Expression of various genes such as sonic hedgehog (Shh), bone morphogenetic protein (BMP) 7, HNF3β, and Vangl-1 emanating from the notochord and floor plate is thought to cause cell specification which influences the morphogenesis of the neural tube [106, 107, 112, 113, 252]. The floor plate and notochord appear to control the pattern of cell types that appear along the dorsoventral axis of the neural tube [226, 278]. Morphogenesis of the spinal neural tube, in particular, the formation of the median hinge point (MHP), is most likely a nonneuroepithelial cell autonomous action as it is dependent on the differentiation of ventral cell types by signals transmitted from axial mesodermal cells of the notochord to overlying neuroepithelial cells [278–284].