128 



THE INTERNAL ENVIRONMENT OF THE BODY 



Part III 



Opening of duct 

 of sweat gland 



Corneal 

 layer 



•Malpighian 

 layer 



-Hair 

 follicle 



Sebaceous 

 gland 



Erector 



- muscle 



of hair 



—Hair 

 papilla 



Nerve 



"> Sections of coiled tubules of sweat gland 



Fig. 8.2. Section of human skin showing the two layers, epidermis and dermis, 

 characteristic of all vertebrates. The outermost corneal layer of the epidermis com- 

 posed of the horny remains of cells is gradually shed in small bits and replaced by 

 new cells from the growing (Malpighian) layer beneath. Cells of this layer contain 

 the pigment that is responsible for dark complexion. As shown in this figure a hair 

 is a shaft of cells that arises from a layer of epidermal cells that form a narrow 

 pocket in the dermis from the bottom of which a core of cells grows upward and 

 forms the hair shaft. Sensory cells, nerves, and the erector muscle provide for the 

 sensitivity and movement of the hair, and sebaceous glands for the oil. (Courtesy, 

 Gardiner: Principles of General Biology. New York. The Macmillan Co., 1952.) 



