MAN, A MAMMAL 



321 



Structure of the Skin. In man, the outer covering of the 

 skin is composed of two layers. The outer part (called the 

 epidermis) is composed largely of flattened dead cells. It is part 

 of this layer that peels off after sunburn, or that separates from 

 the inner part of the epidermis when a water blister is formed. 

 The inner cells of the epidermis are provided with more or 

 less pigment or coloring matter. It is to the varying quantity 

 of this pigment that the light or dark complexion is due. 

 The inmost layer of the epidermis is made up of small cells which 

 are constantly dividing to form new cells to take the place of 

 those in the outer layer which are lost. 



Sweat-Duct 



(1 

 Horny layer 



| 

 Pigment layer / W^ 



Epidermis 



Subcutaneous layer of 

 connective tissue and /at 



Diagram of a section of the skin. (Highly magnified.) 



The dermis, or inner layer, is largely composed of connective tissue 

 filled with a network of blood vessels and nerves. This layer con- 

 tains the sweat glands, some of the most important glands in the 

 body. Other organs connected with the nervous system, and called 

 the tactile corpuscles," cause this part of the skin to be sensitive to 

 touch. 



Nails and Hairs. Nails are a development from the horny 

 layer of the epidermis. A hair is also an outgrowth of the 

 horny layer, although it is formed in a deep pit or depression in 

 the dermis ; this pit is called the hair follide. 

 HUNT. ES. BIO. 21 



