The exoskeleton consists of hard parts present on the surface of the body. It is found in the invertebrates as well as the vertebrates. Scales, feathers, hair, claws, nails, hoofs and horns are examples of exoskeletal elements in the vertebrates. These structures develop from the epidermis of the skin. They are composed of a nonliving, protein material called keratin or horn. Of these, only hairs and nails occur in man.