Developing feathers
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Longitudinal section of the blastema of a growing feather of a Muscovy Duck (Cairina moschata) (HE):detail
The epidermal collar at the lateral side of the papilla of a growing feather develops into three layers: an inner, basilar layer that will give rise to the outer pulp membrane, an intermediate layer that will give rise consecutively to the barbs, the wall of the rachis and the wall of the calamus, and an outer layer that gives rise to the feather sheath, a corneous layer that encloses the growing feather but disappears afterwards.