THE SKIN 267 



12 1). The epidermis contains no nerves and is therefore 

 non-sensitive. The hair and the nails are important 

 modifications of the epidermis. 



A Hair is a slender cylinder, formed by the union of 

 epidermal cells, which grows from a kind of pit in the 

 dermis, called the hair follicle. The oval and somewhat 

 enlarged part of the hair within the follicle is called the 

 root, or bulb, and the uniform cylinder beyond the follicle 

 is called the shaft. Connected with the sides of the follicles 

 are the oil, or sebaceous, glands (Figs. 121 and 122). 

 These secrete an oily liquid which keeps the hair and 

 cuticle soft and pliable. Attached to the inner ends of the 

 follicles are small, involuntary muscles whose contractions 

 cause the roughened condition of the skin that occurs on 

 exposure to cold. 



A Nail is a tough and rather horny plate of epidermal 

 tissue which grows from a depression in the dermis, called 

 the matrix. The back part of the nail 

 is known as the root, the middle convex 

 portion as the body, and the front margin 

 a.s the. free edge (\g. 123). Material for 

 the growth of the nail is derived from 



the matrix, which is lined with active FIG. 123. Section 

 , . ... .. , of end of finger show- 



epidermal cells and is richly supplied ing nail in position. 



with blood vessels. Cells added to the 

 root cause the nail to grow in length (forward) and cells 

 added to the under surface cause it to grow in thickness. 

 The cuticle adheres to the nail around its entire circum- 

 ference so that the covering over the dermis is complete. 



Functions of the Skin. The chief function of the skin 

 is that of protection. It is able to protect the body on 

 account of the tough connective tissue in the dermis, the 

 non-sensitive cells of the epidermis, and also by the touch 



