394 



THE ORGANS 





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PKv i 





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in small hairs, and in Liic large hairs does not extend throughout their 

 entire length. It is from i6 to 2o/< mr'chameter, and consists of from 

 two to four layers of polygonal ottlimboidal cells with finely granular, 

 usually pigmented protoplasrH^yand rudimentary nuclei. 



(2) The cortex makes up the main 

 bulk of the hair and consists of several 

 layers of long spindle-shaped cells, the 

 protoplasm of which shows distinct 

 longitudinal striations, while the 

 nuclei appear atrophied. As these 

 striations give the hair the appear- 

 ance of being composed of fibrillae, 

 the term "cortical fibres" has been 

 applied to them. In colored hair, 

 pigment granules and pigment in 

 solution are found in and between the 

 cells of this layer. This pigment de- 

 termines the color of the hair. In 

 the root the cortical cells are less 

 flattened than in the shaft. 



(3) The cuticle has a thickness of 

 about i«, and consists of clear scale- 

 like, non-nucleated epithelial cells. 

 These overlap one another like 

 shingles on a roof, giving to the sur- 

 face of the hair a serrated appear- 

 ance (Fig. 279). 



The Hair Follicle.— This is 

 also a modification of the skin. In 

 the formation of the follicles of the 

 finer (lanugo) hairs the epidermis 

 alone is concerned. The follicles of 

 the larger hairs contain both epi- 

 dermal and dermal elements. The latter form the connective-tissue 

 follicle, while the epidermis forms the root sheaths. 



(i) The root sheaih consists of two sub-layers — the inner root 

 sheath and the outer root sheath (Figs. 280, 281 and 282). 



(a) The inner root sheath consists of three layers, which from 

 within outward are the cuticle of the root sheath, Hu.xley's layer, and 

 Henle's layer. 



Fig. 278. — Longitudinal Section 

 of Hair and its Follicle from Vertical 

 Section of Scalp. (Ranvier.) a, 

 Shaft of hair; b, derma; c, arrector 

 pili muscle; d, sebaceous gland; e, 

 outer root sheath; /, inner root 

 sheath; g, connective-tissue follicle; 

 h, vitreous membrane; /, hair bulb; 

 j, papilla; s, epidermis. 



