What belongs to the horny formations of the skin? What layer of the skin are they derived from?

The human body is amazing. It is an incredibly complex structure that is fraught with many interesting possibilities. For example, to the question “what are horny formations of the skin?” few people know the answer. And it is incredibly simple. These include: hair, nails, bristles, feathers in birds, horns and wool in animals, shells, needles on the backs of porcupines and hedgehogs are also horny formations of the skin.
These are all derivatives of the epidermis.