STRUCTURE OF THE HAIRS 



313 





of the three membranes and is closely connected with the corium. Next 

 to this, is a fibrous membrane composed of fusiform nucleated fibres 

 arranged transversely. These resemble non-striated muscular fibres. 

 The internal membrane is structureless and cor- 

 responds to the amorphous layer of the true skin. 

 The papilla at the bottom of the hair-sac varies 

 in size with the size of the hairs and is connected 

 with the fibrous layers of the walls of the follicle. 

 It is composed of amorphous matter, with a few 

 granules and nuclei, and it probably contains 

 bloodvessels and nerves, although these are not 

 very distinct. 



The investment of the root of the hair pre- 

 sents two distinct layers called the external and 

 internal root-sheaths. The external root-sheath 

 is three or four times as thick as the inner mem- 

 brane, and it corresponds exactly to the Malpi- 

 ghian layer of the epidermis. This sheath is 

 continuous with the bulb of the hair. The in- 

 ternal root-sheath is a transparent membrane com- 

 posed of flattened cells, usually without nuclei. 

 This extends from the bottom of the hair-follicle 

 and covers the lower two-thirds of the root (see 

 Plate VI). 



Structure of the Hairs. The different varie- 

 ties of hairs present certain peculiarities in their 

 anatomy, but they are all composed of a fibrous 

 structure forming the greater part of their sub- 

 stance, covered by a thin layer of imbricated cells. 

 In the short stiff hairs and in the long white 

 hairs, there is a distinct medullary substance ; 

 but this is wanting in the downy hairs and is Fig 68> _ Root O f the hai 

 indistinct in many of the long dark hairs. 



The fibrous substance of the hairs is com- 

 posed of hard, elongated, longitudinal fibres, 4, opening of the follicle ; 5,5, 



, . , , . , ^ , .^, ,, .j r internal root-sheath ; 6, exter- 



which can not be isolated without the aid of nal root . shea ,h ; 7i 7 , S eba- 

 reagents. They may be separated, however, by ceous glands; 8, 8, excretory 



.ft ., ducts of the sebaceous glands. 



maceration in warm sulphuric acid, when they 



present themselves in the form of dark irregular spindle-shaped plates. 

 These contain pigmentary matter of various shades of color, occasional 

 cavities filled with air and a few nuclei. The pigment may be of any 

 shade between a light yellow and an intense black ; and it is this sub- 



