Cells of primitive node move inwards and form the ‘notochord’. Ectodermal cells overlying notochord differentiate to form neuroectoderm. Neuroectoderm proliferates and form neural plate, neural groove and then ‘neural tube’. Cell at the junction of neuroectoderm and ectoderm differentiate to form ‘neural crest cells’. The neural crest cells lie dorsolateral to neural tube. Intraembryonic mesoderm divides in 3 parts: 1. Paraxial mesoderm, 2. Intermediate mesoderm, and 3. Lateral plate mesoderm. Paraxial mesoderm is segmented to form somites. Intraembryonic coelom develops in lateral plate mesoderm. Folding of embryo converts a disk like embryo into a cylindrical form.