Final answer:
The portion of the nail found under the skin at the base and inside the mantle is known as the nail root, which is essential for the growth of the nail.
Step-by-step explanation:
Attached at the base of the nail, under the skin and inside the mantle is the nail root. The nail root is part of the nail that is lodged deep in the epidermis from which the nail grows. It is located at the proximal end of the nail and is where stem cells in the nail matrix divide to form keratinocytes, which then produce keratin and contribute to the formation of the nail. The nail matrix surrounds the nail root, enabling the nail to grow continuously.