NAILS 



359 



is due to pigment cells lying in the 

 hair shaft. 



Attached to the sides of the 

 hair follicle are oblique strips of 

 unstriped muscle by means of 

 which the hair may be moved. 

 "When these muscles are con- 

 tracted by cold, the skin becomes 

 roughened, and this condition is 

 due to the erection of the hairs. 

 Opening into the side of each hair 

 foUicle is the duct of a sebaceous 

 gland. The glossy appearance of 

 the hair is due to the oil poured 

 out by this gland. 



Hairs may be found on practi- 

 cally all parts of the skin except 

 the sole of the foot and the palm 

 of the hand. Their development 

 varies greatly with the individual. 

 On the head they form a good 

 protection from blows. 



Nails. — The ends of the fingers 

 and toes are protected by thicken- 

 ings of the horny layer of the 

 epidermis called nails. These nails ^^''- ^^^- -section of a hair; h, 



hair shaft showing central 



are very similar to hairs in their 



formation. Their relation to the 



epidermal and dermal layers is 



shown in Figure 166. The base is 



embedded in a fold of the skin, and at its root is a portion 



of the dermis called the matrix which, by pushing out 



medulla or core; d, sehaceous 

 gland; w, sheath of skin; /, 

 fatter tissue. At the base of 

 the hair is seen the papilla 

 which forms it. 



