The skin may be briefly described as a dense layer, consisting chiefly of white fibrous tissue, with which are intermingled yellow elastic and unstriped muscular fibres. It is abundantly supplied with blood-vessels, lymphatics and nerves. Its outer surface is thrown up into little elevations, called papillæ, in which are lodged the tactile corpuscles. Sebaceous and sudoriparous glands are embedded in its substance, while its exterior is protected by an epithelial covering divisible into four strata. The epithelial cells constituting the superficial layer are hard and dry, from loss of water and conversion of albumin into keratin. The cuticular appendages, hair and nails, are merely modifications of the epithelium.
The epithelial sheath, known as the cuticle or epidermis, is destitute of blood-vessels or nerves, and nourished solely by imbibition. The cells dry, harden and flatten as they approach the surface, and are continually being shed as they lose their vitality. The