CHAPTER XVI 

 THE SKIN 



PROTECTIVE coverings are found at all the exposed sur- 

 faces of the body. These vary considerably at different 

 places, each being adapted to the conditions under which 

 it serves. The most important ones are the skin, which 

 covers the entire external surface of the body; the mucous 

 membrane, which lines all the cavities that communicate 

 by openings with the external surface; and the serous 

 membrane, which, including the synovial membranes, lines 

 all the closed cavities of the body. In addition to the 

 protection which it affords, the skin is one of the means 

 by which the body is brought into proper relations with 

 its surroundings. It is because of this function that we 

 take up the study of the skin at this time. 



The Skin is one of the most complex structures of the 

 body, and serves several distinct purposes. It is estimated 

 to have an area of from 14 to 16 square feet, and to have 

 a thickness which varies from less than one eighth to 

 more than one fourth of an inch. It is thickest on the 

 palms of the hands and the soles of the feet, the places 

 where it is most subject to wear. It is made up of two 

 distinct layers an outer layer called the epidermis, or 

 cuticle, and an inner layer called the dermis, or cutis vera 

 (Fig. 12 1). 



The Dermis. This is the thicker and heavier of the 

 two layers, and is made up chiefly of connective tissue. 

 The network of tough fibers which this tissue supplies, 



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