Final answer:
The skin moves easily over underlying muscles due to the loose connective tissue within the hypodermis, which connects the skin to underlying structures and provides insulation and cushioning.
Step-by-step explanation:
The skin can move easily over the underlying muscles because of the loose connective tissue within the hypodermis. The hypodermis, also known as the subcutaneous layer or superficial fascia, is a layer directly below the dermis. It connects the skin to the underlying fascia of bones and muscles with its well-vascularized, loose, areolar connective tissue and adipose tissue, which provides insulation, cushioning, and serves as a mode of fat storage.
The dermis, on the other hand, is the layer directly under the epidermis, serving in a capacity that provides strength and elasticity with collagen and elastin fibers, but it is not responsible for the ease of skin movement over muscles. Additionally, while the epidermis is the outermost layer of the skin providing a protective barrier, it does not play a role in the movement of skin over muscle.