THE APPENDAGES OF THE SKIN 



1161 



The Hairs (pili) (Figs. 878 and 879) are peculiar modifications of the epi- 

 dermis, and consist essentially of the same structure as that membrane. They 

 are found on nearly every part of the surface of the body, excepting the palms of 

 the hands, soles of the feet, the nipples, the inner surface of the prepuce, and the 

 glans penis. Hairs include hairs of the head (capilli); of the eyebrows (xupercilia); 

 of the beard (barba); of the ears (tragi); of the nostrils (vibrisscc); the eyelashes 

 (cilia); hairs of the axilla (hirci); of the pubes (pubes); and the small hairs of the 

 skin or woolly hairs (lanugd). They vary much in length, thickness, and color 

 in different parts of the body and in different races of mankind. . In some parts, 

 as in the skin of the eyelids, they are so short as not to project beyond the follicles 

 containing them; in others, as upon the scalp, they are of considerable length; 

 again, in other parts, as the eyelashes, the hairs of the pubic region, and the whis- 

 kers and beard, they are remarkable for their thickness. Straight hairs are stronger 



EPIDERMIS- 



CORIUM- '-, 



SUBCUTANEOUS^ 

 AREOLAR TISSUE 



RETINACULA 

 OF SKIN 



OCCIPITO- FRONTAL 

 APONEUROSIS 



ARRECTOR 

 PILI MUSCLE 



..SEBACEOUS 

 GLAND 



SUDORIFEROUS 

 GLAND 



--HAIR FOLLICLE: 

 ROOT 



'HAIR KNOB 



T-HAIR BULB 



FIG. 878. Vertical section through the skin of the head. The hairs of the head in longitudinal section. (Toldt.> 



than curly hairs, and present on transverse section a cylindrical or oval outline; 

 curly hairs, on the other hand, are flattened. The hairs are usually oblique to 

 the surface frorn which they arise (Fig. 878). Their direction depends upon the 

 region from which they spring, being fairly regular in certain regions. Thus 

 are formed hair streams (flumina pilorum) and hair whirlpools (vortices pilorum). 



A hair consists of the root, the part implanted in the skin; the shaft, the portion 

 projecting from its surface; and the point. 



The root of the hair (radix pili) presents at its extremity a bulbous enlargement, 

 the hair bulb (bulbuspili) (Fig. 877), which is whiter in color and softer in texture 

 than the shaft, and is lodged in a follicular involution of the epidermis called the 

 hair follicle (folliculus pili) (Fig. 868). When the hair is of considerable length 

 the follicle extends into the subcutaneous cellular tissue. The hair follicle com- 

 mences on the surface of the skin with a funnel-shaped opening, and passes inward 

 in an oblique or curved direction the latter in curly hair to become dilated at 

 its deep extremity or fundus (fundus folliculi pili), where it corresponds with the 

 bulbous condition of the hair which it contains. It has opening into it, near its 

 free extremity, the orifices of the ducts of one or more sebaceous glands (Figs. 

 877 and 878). At the bottom of each hair follicle is a small, conical, vascular 

 eminence or papilla, the hair papilla (papilla pili) (Figs. 877 and 878), similar 

 in every respect to the papilla found upon the surface of the skin; it is continuous 

 with the dermic layer of the follicle, is highly vascular, and is probably supplied 



