HAIR. 



C 374 ] 



HAIR. 



The hair-follicles are pouches, about 1-10 

 to 1-4" in length, pretty closely surrounding 

 the hairs, and extending in the short hairs 

 into the substance of the upper layer of the 

 cutis ; but in the long hairs, into its deepest 

 portion, or even into the subcutaneous cel- 

 lular tissue. They may be regarded as pro- 

 longations of the skin, with its components, 

 the cutis, basement-membrane, and epider- 

 mis. Hence three parts are distinguishable 

 in them : an external, fibrous, very vascular 

 portion the proper hair- follicle ; a base- 

 ment-membrane ; and a non- vascular cellu- 

 lar coat the epidermis of the follicle, or, 

 because it surrounds the root of the hair, 

 the root-sheath. 



The fibrous portion of the follicle con- 

 sists of two layers or membranes. The 

 outer one (fig. 292^) is the thicker, and 

 contains vessels and nerves. Its inner sur- 

 face is connected with the inner layer; ex- 

 ternally it is attached to the surrounding 

 areolar tissue ; and above, it is continuous 

 with the outer layer of the cutis. It con- 

 sists of common areolar tissue, the fibres 

 of which are longitudinal, with elongated 

 spindle-shaped nuclei. The inner layer 

 (fig. 300 0) is much more delicate, and only 

 extends from the base of the hair-follicle 

 to the orifice of the sebaceous follicles. It 

 consists of a single layer of transverse fibres, 

 with long and narrow nuclei, resembling 

 unstriated muscular fibres. 



The third layer (fig. 300 6), or basement- 

 membrane, is transparent and structureless, 

 and extends from the base of the follicle, 

 without apparently covering the papilla, as 

 far as the inner root-sheath, and perhaps 

 higher. It presents delicate transverse 

 anastomosing lines, producing a fibrous 

 appearance. 



The pulp or papilla of the hair (fig. 292 i) 

 belongs to the follicle, and corresponds to a 

 papilla of the skin. It is rounded or oval, 

 1-96 to 1-480" in length, is connected with 

 the fibrous coat of the follicle by a kind of 

 stalk, and consists of indistinctly fibrous 

 areolar tissue with nuclei and granules of 

 fat, but contains no cells. 



The two root-sheaths consist of the epi- 

 dermic covering of the hair-follicle. The 

 outer (fig. 292/) is the continuation of the 

 rete mucosum of the skin, and lines the 

 entire follicle. Its lower part is in contact 

 externally with the basement-membrane of 

 the follicle; but above the termination of 

 the inner transverse layer of the follicle, it 

 is in direct contact with the outer or longi- 



tudinal layer. It consists of several layers 

 of nucleated cells, resembling those of the 

 rete mucosum of the skin, the outer having 

 their long axis perpendicular to that of the 

 hair, the others, especially towards the bulb, 

 being rounded. This outer root-sheath is 

 most distinct in the follicles of the skin of 

 the negro, from which it may be withdrawn 

 with the epidermis after maceration. 



Fig. 300. 



Magnified 300 diameters. 



Portion of the inner fibrous coat and basement-mem- 

 brane of a hair-follicle : a, inner coat with transverse 

 fibres and elongated transverse nuclei; b, basement- 

 membrane, seen as it were in section ; c, its lacerated 

 margins ; d, fine lines (fibres?) on its inner surface. 



The inner root-sheath '(fig. 299, e,f) forms 

 a transparent, very firm and elastic, yellow- 

 ish membrane, extending from near the base 

 of the hair-follicle to near the mouths of the 

 sebaceous follicles, where it terminates ab- 

 ruptly with a jagged margin. Externally 

 it is connected with the outer root-sheath, 

 internally with the outer layer of the cuticle 

 of the hair ; hence no interval exists natu- 

 rally between it and the hair. At first sight 

 it appears as a perfectly homogeneous mem- 

 brane, but on closer examination it is seen 

 to be distinctly cellular ; it consists of two 



