The middle layer of the skin is called the __________.

The middle layer of the skin is referred to as the dermis, which plays a vital role in supporting the skin's structure and function. It contains connective tissue, blood vessels, lymphatic vessels, nerve endings, and various skin appendages such as hair follicles and sweat glands. The dermis serves as a critical layer that provides strength, elasticity, and nourishment to the epidermis, the outermost skin layer.

Understanding the roles of other layers helps clarify why the dermis is the correct answer. The hypodermis, or subcutaneous layer, is located beneath the dermis and consists primarily of fat and connective tissue, functioning mainly for insulation and cushioning. The epithelium generally refers to the cell layers that line surfaces in the body, including those of organs and cavities, while the epidermis specifically is the outermost layer of skin that acts as a barrier to protect the underlying tissues from foreign substances. Thus, the dermis is distinct as the middle layer, making it the correct choice.