Final answer:
The presence of the stratum lucidum and the thickness of the stratum corneum are key determinants of skin thickness, with both layers being most prominent in the thick skin of the palms, soles, and digits.
Step-by-step explanation:
The thickness of skin is largely determined by the presence of the stratum lucidum and the thickness of the stratum corneum.
The stratum lucidum is a layer of the epidermis found only in thick skin, such as that on the palms, soles, and digits. It consists of dead, flattened keratinocytes densely packed with a clear protein called eleidin, which provides a barrier to water and adds to the thickness of the skin.
Above the stratum lucidum is the stratum corneum, which contributes significantly to skin thickness and consists of dead cells that continuously shed and are replaced by cells from deeper layers of the epidermis.