Which structure cannot be found in the dermis of the skin?

The structure that cannot be found in the dermis of the skin is keratin. Keratin is a type of protein that is primarily found in the epidermis, the outermost layer of the skin. It is crucial for the formation of hair, nails, and the outer layer of the skin, providing strength and water resistance.

In contrast, collagen fibers are abundant in the dermis, contributing to the skin's strength and elasticity. Nerve endings are also located in the dermis, allowing for sensory perception, including touch and temperature. Blood vessels are another essential component found within the dermis, supplying nutrients and oxygen to the skin and helping with thermoregulation.

Thus, the presence of keratin in the epidermis rather than the dermis highlights its role in skin structure and function, while the other listed structures are integral components of the dermal layer.