The trilaminar embryo at the start of the third week of gestation consists of dorsal ectoderm with, sequentially, deeper mesoderm and then endoderm.
The epithelial lateral ectoderm gives rise to the epidermis. This is ectoderm which has escaped induction to form neural tissue by underlying axial mesoderm. The ectoderm seems to give rise to its appendages after induction by regional mesoderm.
The dermis derives from the paraxial mesoderm. The latter eventually forms somites, cyclical structures which are symmetrical about the primitive neural tube. The dorsolateral section of each somite, the dermatome, has cells which segmentally migrate under the ectoderm to form dermal precursors.
The region between neural and non-neural ectoderm is the origin of the neural crest. Cells from this region have complex migratory paths and pluripotential fates. After migration, they convert to various cell types within the skin including melanocytes, sensory and autonomic nerve cells.
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