SPINOSUM
As best I can tell it seems to be a typo or OCR error for "stratum corneum," which is the outermost layer of skin cells.
corneum is the most superficial layer of the epidermis. the basale layer is the deepest layer of the epidermis
The English term 'stratum basale' means the innermost layer of the epidermis
Yes. The plural is strata (both are pronounced with a long "a", as Straytum, or Strayta).