Final answer:
The dermis is not an accessory structure of the skin; it is a layer that contains the accessory structures such as hair follicles, sweat glands, and sebaceous glands.
Step-by-step explanation:
The accessory structures of the skin include hair follicles, sweat glands, and sebaceous glands. These structures originate from the epidermis and serve various functions such as protecting the skin, regulating body temperature, and producing sebum for hair. In contrast, the dermis is not an accessory structure, but rather a constituent layer of the skin itself that contains connective tissue, blood vessels, nerves, and is home to the aforementioned accessory structures. Therefore, the answer to which of these is NOT an accessory structure of the skin is C) dermis.