Anatomy of the Normal Skin
The skin can be divided into three main functional areas. These are the:
epidermis – the major protective layer derived from the fetal ectoderm;
dermis – the major support layer – of mesodermal original;
skin appendages composed of cells derived from both ectoderm and mesoderm (hair follicle, sebaceous gland, apocrine sweat gland, eccrine sweat gland, and nails).
in addition a fourth area, the subcutaneous fat, may be involved in deeply situated skin lesions such as erythema nodosum.