Figure 1.

Anatomy of the epidermis. (1) The cornified layer (stratum corneum)—the outermost layer of the skin—is composed of keratin, a fibrous protein. (2) The clear/translucent layer (stratum lucidum) is present only in the thick skin of the palms and soles. (3) The granular layer (stratum granulosum) consists of keratinocytes with granular cytoplasm and no nuclei. (4) The spinous layer (stratum spinosum) consists of keratinocytes derived from cells produced in the basal layer. Keratin production starts here. (5) The basal layer (stratum basale) is the innermost layer of the epidermis. The cells of this layer produce the keratinocytes that comprise the spinous layer. The basal layer is the site of basal cell carcinoma. (Adapted from Lewis WH, ed. Gray’s Anatomy of the Human Body, 20th ed, 1918.⁸)