2^2 NORMAL HISTOLOGY. 



polyhedral cells, whose protoplasm is very faintly granular and whose 

 nuclei are wanting. Next follows Huxley's layer, consisting of a 

 single or double row of shorter and broader polyhedral cells, which 

 ordinarily display small nuclei ; at the lower part of the follicle these 

 cells contain numerous granules, probably of eleidin. Of the 15-35 

 fj. representing the entire thickness of the inner root-sheath, Henle's 

 layer contributes about one-third, the remaining two-thirds being 

 made up by the layer of Huxley. The outer surface of Huxley's 

 layer is covered with the clear delicate cuticle of the root-sheath, 

 a single layer of thin transparent plates lying against the cuticle of 

 the hair in such close relation that the two cuticular layers appear as 

 one. The cells of this envelope are imbricated in a manner similar 

 to those of the hair-cuticle, but the free edges of the plates are di- 

 rected in the opposite direction from those of the hair, the serrations 

 of the cuticle of the root-sheath fitting into the impressions on the 

 surface of the hair. 



The extremity or base of the hair-follicle presents a deep invagina- 

 tion for the reception of the process of dermal connective tissue con- 

 stituting the hair-papilla. The latter is a large, simple, club-shaped 

 elevation, . i--3 mm. in length, which usually contains numerous 

 branched pigment-cells and loops of blood-vessels. The presence 

 of nerves within the papillae, on the contrary, is very doubtful. 



The most interesting as well as important part of the hair-follicle 

 is immediately around the hair-papillae, since to the differentia- 

 tion of the soft granular polyhedral cells occupying this position the 

 hair, together with the inner root-sheath, owes its formation. These 

 elements are the direct derivatives of the stratum mucosum, 

 and represent the centre of greatest activity ; the elements di- 

 rectly over the papilla supply the material from which the hair proper 

 is developed, while the cells at the lower part of its sides become 

 transformed into the layers of the inner root-sheath. For some dis- 

 tance immediately above the summit of the papilla, polyhedral nu- 

 cleated granular, and often pigmented, cells compose a matrix from 

 which the constituents of the cortical and medullary portions of the 

 hair are directly derived. 



The muscles of the hairs, the arrectores pilorum, exist as 

 minute flattened plexiform bundles of non-striped muscle, which 

 extend from the most superficial parts of the corium to the hair- 

 follicles ; the muscular band is attached to the fibrous coat of the 

 follicle, below the sebaceous glands, on the side towards which the 

 hair is directed. When the muscle contracts the obliquely-placed 

 follicle becomes perpendicular and the shaft erect, in consequence of 

 which the integument attached about the hair is drawn up, producing 

 the well-known condition of cutis anserina, or "goose-flesh." 



