Final answer:
The deep fold of skin in which Mary's nail root is lodged is called the nail fold. It helps to anchor the nail body in place and forms the nail cuticle.
Step-by-step explanation:
The deep fold of skin in which Mary's nail root is lodged is called the nail fold. The nail fold is a groove in the skin where the side edges of the nail plate are embedded. It helps to anchor the nail body in place. The nail fold that meets the proximal end of the nail body forms the nail cuticle, also known as the eponychium.