After implantation of the blastocyst, embryonic cells divide further. At the end of week 2, three germ layers are formed. The ectoderm is the outermost layer of the early embryo: ectoderm – mesoderm – endoderm. The ectoderm will form skin, hair, nails, teeth, epithelium of mouth and nose, the peripheral nervous system, brain, motor neurons, retina and much more (Hill, 2020).