Final answer:
The lunula is the visible part of the nail matrix, a crescent-shaped layer of thick epithelium at the base of the nail where the nail bed meets, essential for nail growth. Therefore, the correct option is 2.
Step-by-step explanation:
The lunula is the half-moon shape at the base of the nail and is the visible part of the nail matrix where the nail bed meets. The lunula is a crescent-shaped layer of thick epithelium which appears white because it overlies the thickened underlying nail matrix that obscures the blood vessels beneath. The nail matrix is a deep layer of living epidermal tissue that contains stem cells which divide to produce new nail cells. These new cells become keratinized to form the nail body - mainly the nail plate - that progressively emerges from under the cuticle as the nail grows. The lunula's visibility can vary among individuals but is an essential part of nail growth.
The nail bed rich in blood vessels gives most of the nail its characteristic pink color, except for the lunula. Meanwhile, structures like the nail root, fold, and cuticle (or eponychium) also play vital roles in nail health and structure, with the nail root being lodged deep in the epidermis from which the nail grows.