“The epidermis is composed of several layers: The stratum basale or stratum germinativum undergoes constant mitosis to replace the cells exfoliated from the skin's surface. The new cells push up into the intervening or transitional layers toward the surface. The stratum spinosum or "spiny layer" consists of cells attached to one another by fibrous desmosomes which enable the skin to be pulled and stretched without the cells pulling apart. As the cells push up through these layers they accumulate large amounts of keratin and keratohyaline (a glycoprotein) and this substance forms dense granules in the stratum granulosum. As these cells reach the surface they exfoliate, or slough off. In keratinized skin the cells die and become hard, flattened cells completely filled with keratin and keratohyaline. This produces a cornified (horny) outer layer. When this layer thickens as a result of constant pressure it produces “corns” and calluses seen on the feet and hands.