Fig. 5.
Schematic of feather follicle structure. Feathers initially form as a cylinder. The mesenchymal structures (shades of red) are the dermal papilla (dp) and the pulp. Blood vessels (bv) bring nutrients to the growing feather follicles. The epithelia (shades of blue) will form the feather. The epithelial localized growth zone (LoGZ) is near the base of the feather above the dermal papilla. Feather branching into barbs takes place in the differentiating ramogenic zone (rz). After differentiation, the pulp cells die, enabling the feather branches to open up.