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HAND-BOOK OF PHYSIOLOGY. 



edges turned upward (Fig. 233, 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 com- 



FIG. 233. Surface of a white hair, magnified 160 diameters. The wave lines mark the upper or 

 free edges of the cortical scales. J5, separated scales, magnified 350 diameters. (Kolliker.) 



monly, in the human subject, occupies the whole of the inside of the hair; 



but in some cases there is left a small central space filled by a substance 



called the medulla or pitli, composed of small 

 collections of irregularly shaped cells, contain- 

 ing sometimes pigment granules or fat, but 

 mostly air. 



The follicle, in which the root of each hair 

 is contained (Fig. 235), forms a tubular de- 

 pression from the surface of the skin, descend- 

 ing into the subcutaneous fat, generally to a 

 greater depth than the sudoriferous 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 epi- 

 thelium, continuous with those of the epider- 

 mis, and its walls are formed of pellucid mem- 

 brane, which commonly, in the follicles of the 

 largest hairs, has the structure of vascular 

 fibrous tissue. At the bottom of the follicle is 

 a small papilla, or projection of true skin, and 

 it is by the production and out-growth of epi- 

 dermal cells from the surface of this papilla 

 that the hair is formed. The inner wall of the 

 follicle is lined by epidermal cells continuous 

 with those covering the general surface of the 

 skin; as if indeed the follicle had been formed 

 by a simple thrusting in of the surface of the 

 integument (Fig. 234). This epidermal lining 

 of the hair follicle, or root-sheath of the hair, 

 (Kolliker.) See ^ composed of two layers, the inner one of 



c, knob; d, hair cuticle; e, internal, 

 and /, external root-sheath; gi, /i, 

 dermic coat of follicle; i, papilla; 

 k, k, ducts of sebaceous glands; I, 

 corium; m, mucous layer of epi- 

 dermis; o, upper limit of internal 



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