THE SKIN 



353 



this removal of body wastes are grouped together under 

 the name of the excretory system. The hings, by remov- 

 ing the carbon dioxide, may be inckxded in this system, 

 but the removal of the principal body wastes is the work 

 of the kidneys and the skin. 



The skin. — If we examine the surface of the body care- 

 fully we find it everywhere covered with a layer of flexible, 

 elastic tissue which we call the skin. The hair and nails 

 are modifications of this tissue and are included in the 

 study of skin structure. 



Examination of a section of the skin taken from any 

 surface of the body shows it to consist of two distinct 

 layers. The upper layer (epidermis, or cuticle) is thinner 



Homy layer 

 Pigment layer 



Tactile Organs 



Nerve — 



Blooi Vessels -■ 



Sweat Gland'Z:^ 



Fig. 161 — Diagi-am of a section of skin. 



than the lower layer (dermis, or corium), and contains no 



blood vessels. Hence, it is possible to prick and even tear 



off portions of the epidermis without causing bleeding. 



-This epidermal layer varies greatly in thickness in different 



EDDT. PHYS, 



