Once the three germ layers have been established, cellular differentiation can occur. The first major process here is neurulation, wherein the ectoderm differentiates to form the neural tube, neural crest cells and the epidermis. Each of these three components will give rise to a particular compliment of cells. The neural tube cells give rise to the central nervous system, neural crest cells give rise to the peripheral and enteric nervous system, melanocytes, and facial cartilage, and the epidermal region will give rise to the epidermis, hair, nails, sebaceous glands, olfactory and oral epithelium, and eyes.