The ectoderm is outermost of the three germ layers of the developing embryo, the other two being the mesoderm and the endoderm. The ectoderm, like the other two layers, forms at the gastrulation stage in embryonic development (when the digestive system is developing). It forms from the epiblast .

In vertebrates, the ectoderm can be distinguished as three parts, each giving rise to different tissues:

• External ectoderm
  • Skin (along with glands, hair, nails)
  • Mouth and nasal cavity epithelium
  • lens and cornea of the eye

• Cells of the neural crest
  • Melanocytes
  • Peripheral Nervous System
  • Facial cartilage and teeth dentine

• Neural tube
  • Brain (rhombencephalon , mesencephalon and prosencephalon)
  • Spinal cord and motor neurons
  • the retina
  • Pituitary

See also: neurulation.