The ectoderm originates in the epiblast, and is formed during gastrulation. Once the mesoderm forms, cells cease to ingress into the primitive streak; the remaining epiblast cells are hereafter called ectoderm. The ectoderm gives rise to two distinct lineages, namely, the surface ectoderm and the neural ectoderm.
The ectoderm forms the central and peripheral nervous systems and epidermis, and contributes to the adipose and heart as well as to numerous other organs. The ectoderm forms many of the sensory organs (eye, ear, nose), and is also the source of Rathke's pouch, an invaginating diverticulum of the stomodeal roof which ultimately detaches from the stomodeum and becomes the adenohypophysis of the pituitary gland.