PHYSIOLOGICAL ANATOMY OF THE HAIRS. 



387 



the form of a sheath. The study of these parts is much simplified by keeping constant- 

 ly in view the correspondence between the different layers of the follicles and the layers 

 of the true skin, and the relations of the root -sheaths with the epidermis. 



The follicles are tubular inversions of the structures that compose the corium, and 

 their walls present three membranes. Their length is from T ^ to of an inch. The 



FIG. 107. Hair and A air-follicle. (Sappey.) Fro. 108. Root of the Jiair. (Sappey.) 



:, root of the hair: 2, bulb of the hair, covering the papilla 1, root of the hair; 2, hair-bulb; 3, pa- 



of the hair-follicle ; 3, internal root-sheath ; 4, external pilla of the follicle ; 4, opening of 



root-sheath; 5, membrane of the hair-follicle, composed the follicle ; 5, 5, internal root-sheath; 



of fusiform, nucleated fibres arranged transversely (the 6, external root-sheath ; 7, 7, sebace- 



internal, amorphous membrane of the follicle is very deli- . ous glands ; 8, 8, excretory ducts of 



cate and is not represented in the figure) ; 6, external the sebaceous glands, 



membrane of the follicle, composed chiefly of longitudinal 

 fibres : 7, 7, muscular bands attached to the follicle ; 8, 8, 

 extremities of these bands passing to the skin ; 9, com- 

 pound sebaceous gland, with its duct (10) opening into 

 the upper third of the follicle ; 11, simple sebaceous gland ; 

 12, opening of the hair-follicle. 



membrane that forms the external coat of the follicles is composed of inelastic fibres, 

 arranged for the most part longitudinally, provided with blood-vessels and a few nerves, 

 containing some fibro-plastic elements, but deprived entirely of elastic tissue. This is 



