EPIDERMAL APPENDAGES. 



73 



bulk of tlie root are con- 

 tinued in a column up the 

 centre of the stem, and are 

 termed the medulla. But in 

 the smaller hairs of the body, 

 and even often in the hairs 

 of the head, the medulla is 

 absent, or only present in 

 small patches ; and in all 

 instances the bulk of the 

 stem is of fibrous substance, 

 which, in contradistinction to 

 the medulla, is termed the 

 cortical part. This cortical 

 substance appears in the 

 natural state nearly homo- 

 geneous; but when boiled 

 with potash it is seen to 

 consist of flat fibres, which 

 are derived from the cells 

 of the root by elongation 

 and alteration of consistence. 

 The three elements of the 

 stem of the hair are very dif- 

 ferently represented in differ- 

 ent animals. In wool the 

 edges of the epithelial cells are 

 prominent, and by their ten- 

 dency to catch cause the hairs 

 to be easily felted. In some 

 small animals the epithelium 

 is like a series of hcllow cones 

 embracing the hairs. In some, 

 as in the mouse, the medulla 

 is thrown into a series of air 



Fig. 40. HAIR, a, Papilla in the centre of the bulb ; 5, dermic 

 coat of the hair-follicle ; c, d, outer and inner cuticular lining ; 

 e, cortex of the shaft ; /, medulla ; g, epithelium ; g', the same 

 seen in profile, imbricated on the root ; h, portion of shaft be- 

 come white, showing the medulla enlarged by presence of minute 

 air-bells, reflecting the light, and making the hair thicker. 



