STRUCTURE OF HAIR. 429 



modification of the epidermis. Externally it is covered by 

 a layer of fine scales closely imbricated, or overlapping 

 like the tiles of a house, but with the free edges turned 

 upwards (fig. 1 1 6, A). It is called the cuticle of the hair. 

 Beneath this is a much thicker layer of elongated horny 

 cells, closely packed together so as to resemble a fibrous 

 structure. This, very commonly, in the human subject, 

 occupies the whole of the inside of the hair ; but in some 



Fig 1 1 6.* 



'1 -'"^~^-' V /^ 



cases there is left a small central space filled by a sub- 

 stance called the medulla or pith, composed of small collec- 

 tions of irregularly shaped cells, containing fat- and pig- 

 ment-granules. 



The follicle, in which the root of each hair is contained, 

 (fig. 117) forms a tubular depression from the surface of the 

 skin, descending into the subcutaneous fat, generally to 

 a greater depth than the sudoriparous glands, and at 

 its deepest part enlarging in a bulbous form, and often 

 curving from its previous rectilinear course. It is lined 

 throughout by cells of epithelium, continuous with those 

 of the epidermis, and its walls are formed of pellucid 

 membrane, which commonly, in the follicles of the largest 

 hairs, has the structure of vascular fibre-cellular tissue. 

 At the bottom of the follicle is a small papilla, or projec- 

 tion of true skin, and it is by the production and out- 



* Fig. 116. A, surface of a white liair, magnified 1 60 diameters. The 

 wave lines mark the tipper or free edges of the cortical scales. JB, 

 separated scales, magnified 350 diameters (after Kolliker). 



