CHAPTEK XII. 



THE SKIN AND ITS FUNCTIONS. 



THE skin serves (1), as an external integument for the protection of 

 the deeper tissues, and (2), as a sensitive organ in the exercise of touch; 

 it is also (3), an important excretory, and (4), an absorbing organ; while 

 it plays an important part in (5) the regulation of the temperature of the 

 body. 



Structure of the Skin. The skin consists, principally, of a vascu- 

 lar tissue, named the corium, derma, or cut is vera, and an external cover- 

 ing of epithelium termed the cuticle or epidermis. Within and beneath 

 the corium are imbedded several organs with special function, namely 

 sudoriferous glands, sebaceous glands, and hair follicles; and on its surface 

 are sensitive papilla. The so-called appendages of the skin the hair and 

 nails are modifications of the epidermis. 



Epidermis. The epidermis is composed of several strata of cells of 

 various shapes, and closely resembles in its structure that which lines the 

 mouth. The following four layers may be distinguished. 1. Stratum 

 conieum (Fig. 225, ), consisting of many superposed layers of horny 

 scales. The different thickness of the epidermis in different regions of 

 the body is chiefly due to variations in the thickness of this layer; e.g., 

 on the horny parts of the palms of the hands and soles of the feet it is of 

 great thickness. The stratum corneum of the buccal epithelium chiefly 

 differs from that of the epidermis in the fact that nuclei are to be dis- 

 tinguished in some of the cells even of its most superficial layers. 



2. Stratum lucidum, a bright homogeneous membrane consisting of 

 squamous cells closely arranged, in some of which a nucleus can be seen. 



3. Stratum granulosum, consisting of one layer of flattened cells which 

 appear fusiform in vertical section: they are distinctly nucleated, and a 

 number of granules extend from the nucleus to the margins of the cell. 



4. Stratum Malpighii or Rete mucosum, which consists of many strata, 

 The deepest cells, placed immediately above the ctitis vera, are columnar 

 with oval nuclei: this layer of columnar cells is succeeded by a number 

 of layers of more or less polyhedral cells with spherical nuclei; the cells 

 of the more superficial layers are considerably flattened. The deeper sur- 

 face of the rete mucosum is accurately adapted to the papillae of the 

 true skill, being, as it were, moulded on them. It is very constant in 

 thickness in all parts of the skin. The cells of the middle layers of the 



