CHAPTER VII 



THE FUNCTIONS OF THE SKIN 



The skin is composed of two main parts, the epidermis and 

 dermis. The epidermis is subdivided into the cuticle or stratum 

 corneum and the rete mucosum or Malpighian layer. Neither 

 part of the epidermis contains any blood vessels. 



The cuticular part consists of a stratified epithelium which is 

 being continually given off in flakes. It is hard and horny. 

 The rete mucosum is soft and protoj)lasmic, its cells frequently 

 containing pigment (as in the coloured races of mankind) . Inter- 

 cellular channels conveymg lymph are found in both parts of the 

 epidermis but especially in the rete mucosum. 



The dermis or cutis vera is a dense connective tissue containing 

 numerous blood vessels. Its surface adjoining the epidermis is 

 raised into little more or less rounded elevations called the 

 papillae. These often contain sensory end organs (tactile cor- 

 puscles). Adipose tissue, sweat glands, and the roots of the 

 hair are also present in the dermis in greater or less profusion. 



The hair. A hair consists of horny epithelial cells. The 

 part of it below the surface of the skin is enclosed in a kind of 

 sac or follicle. At the bottom of this sac is the vascular papilla 

 in which the newest portion of the hair develops. The shaft of 

 the hair is developed by the epidermal cells surrounding the 

 papilla becoming converted into horn. The cornified hair cells 

 formed in this way are continually pushed outwards by fresh cells 

 developed from below and the shaft of the hair consequently 

 comes to protrude from the surface. When the hair is fully 

 grown a new hair may arise by budding from the old papilla and 

 sac. The walls of the sac or follicle form the root-sheaths and 

 are composed of epidermal and dermal cells which dip down from 

 the surface, so as to enclose the hair root. The follicle, papilla 

 and root-sheath are provided with nerve fibres, especially well- 

 developed in large tactile hairs (whiskers). The hair shaft (i.e. 

 the hair itself) is composed of a medulla or pith of loose texture 



