What structure holds the epidermis and dermis together?

The dermal papillae are small, nipple-like projections that extend from the dermis into the epidermis, effectively anchoring the two layers of skin together. These structures increase the surface area of contact between the epidermis and dermis, promoting the exchange of nutrients and waste products and enhancing the strength and stability of the skin. The dermal papillae also play a role in important functions such as thermoregulation and sensation, due to the presence of nerve endings and blood vessels.

In contrast, the stratum corneum refers to the outermost layer of the epidermis, primarily composed of dead skin cells, and does not serve to connect the epidermis and dermis. The permeability barrier is related to the skin's ability to prevent water loss and protect against environmental factors, but it does not physically hold the layers together. Lastly, the dermis layers refer to the different regions within the dermis itself (the papillary and reticular layers), which offer structure and support but are not the connecting mechanism between the epidermis and dermis.