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Ectoderm

The "ectoderm" is one of the three primary germ cell layers in the early embryo. The other two layers are the mesoderm (middle layer) and endoderm, with the ectoderm as the most exterior layer. It forms from the outer layer of germ cells.

Ectoderm is the external layer and forms the nervous system, including the brain, spinal cord, peripheral nerves. Ectoderm also gives rise to the skin of the integumentary system, as well as nails, sweat glands, nostrils and anus.

In vertebrates, the ectoderm has three parts: external ectoderm (also known as surface ectoderm), the neural crest, and neural tube. The latter two are known as neuroectoderm.