Final answer:
Nails are the structure also composed of dead keratinocytes and are not fully keratinized. They are found at the tips of fingers and toes and are made of keratin, providing hardness to the nails.
Step-by-step explanation:
The structure also composed of dead keratinocytes, which is not "fully keratinized," refers to the nail. Nails are an accessory organ of the skin made of sheets of dead keratinocytes found at the distal ends of the fingers and toes. While the hair shaft and the stratum corneum of the skin are fully keratinized, the nail is not, although it also consists of dead keratinocytes. Like the hair, nails serve as a protective covering and are composed of keratin, a protein that provides hardness. The process of forming these keratinized structures involves keratinocytes in the epidermis, which manufacture and store keratin.