The innermost layer of the epidermis WordNet 3.0 & Open English WordNet

The stratum basale is the deepest layer of the five layers of the epidermis, the external covering of skin in mammals. Wikipedia

The Malpighian layer of the epidermis, the outermost layer of the skin, is generally defined as both the stratum basale and the thicker stratum spinosum immediately above it as a single unit, although it is occasionally defined as the stratum basale specifically, or the stratum spinosum specifically. Wikipedia

Deepest layer of the five layers of the epidermis Wikidata

contains granules of pigments called melanin and keratin Wikidata

The stratum basale and stratum spinosum of the skin, or sometimes just one of the two. Wiktionary