184 



THE HUMAN MECHANISM 



5. The structure of the skin. The skin is an organ which 

 performs several functions, the most important being (1) that 

 of protecting the underlying structures 

 from drying and mechanical injury ; 

 (2) that of assisting in maintaining the 

 constant internal temperature of the 

 body ; and (3) that of receiving the ex- 

 ternal stimuli of pressure, heat, and cold. 

 Incidentally, as we have seen, the skin 

 is an organ of excretion. We may there- 

 fore describe its structure and excretory 

 function in this connection, reserving 

 the study of its other functions for 

 Chapters XII and XIV. 



The skin consists of an outer layer, 

 the epidermis, and an inner layer, the 

 dermis, cutis, or corium. The clermis 

 consists of connective tissue richly sup- 

 plied with blood vessels, lymphatics, 

 and nerve fibers, together with sense 

 organs of touch. The fiber bundles of 

 the connective tissue are most dense 

 near the epidermis; in the deeper por- 

 tions the network is loose and the lymph 

 FIG. 83. Cross section spaces larger, the connective tissue of 

 the dermis passing insensibly into that of 

 the subcutaneous connective tissue. 



The cells of the more open portions 

 sweat gland; D, dermis; o f the dermal network, and especially 



E, subcutaneous connec- , , 



The those of the subcutaneous tissue, store 



within their CVtO- 

 . J 



plasm. The subcutaneous tissue, indeed, 

 is one of the most important organs in the body for the 

 storage of fat. Connective tissue in which large amounts of 

 fat are stored is known as adipose tissue (see p. 223). 



E 



of skin 



A, horny layer of epi- 

 dermis; B, deeper layer 

 of epidermis ; C, duct of 



tive tissue (p. 7). 



blood vessels are injected up more or } egs 

 to show black. Cf.Fig.89 



