Neurulation occurs in two parts, primary and secondary neurulation. Both processes position neural crest cells between a superficial epidermal layer and the deep neural tube. During primary neurulation, the notochord cells of the mesoderm signal the adjacent, superficial ectoderm cells to reposition themselves into a columnar pattern to form cells of the ectodermal neural plate. As the cells continue to elongate, a group of cells immediately above the notochord change their shape, forming a wedge in the ectodermal region. These special cells are called medial hinge cells (MHPs). Now, as the ectoderm continues to elongate, the ectodermal cells of the neural plate fold inward. The inward folding of the ectoderm by virtue of mainly cell division continues until another group of cells form within the neural plate. These cells are termed dorsolateral hinge cells (DLHPs), and, once formed, the inward folding of the ectoderm stops. The DLHP cells function in a similar fashion as MHP cells regarding their wedge like shape, however, the DLHP cells result in the ectoderm converging. This convergence is led by ectodermal cells above the DLHP cells known as the neural crest. The neural crest cells eventually pull the adjacent ectodermal cells together, which leaves neural crest cells between the prospective epidermis and hollow, neural tube.