THE SKIN AND ITS APPENDAGES. 27 1 



ment, while the latter is derived from a part of the same cells that 

 form the hair itself, and is therefore closely related to the hair. 



The outer root-sheath being the direct continuation of the 

 stratum mucosum of the adjacent skin, its structure corresponds 

 with that layer of the epidermis ; when well developed, as in the 

 follicles of the larger hairs, this sheath measures 40-60 n in thick- 

 ness, or more than twice the breadth of the inner root-sheath. In 

 the upper part of the follicle, where the glassy membrane and the 

 circular fibrous layer are wanting, the outer sheath rests directly in 

 contact with the longitudinal layer. The outer cells of the root- 



FIG. 308. 



Transverse section of hair-follicle from human scalp, more highly magnified : a, substance of hair, 

 condensed at periphery (b) c, cuticular layer, composed of cuticles of hair and*of inner root-sheath ; 

 d, e, respectively layer of Huxley and of Henle ; f, outer root-sheath ; g, glassy membrane ; h, i, 

 circular and loogitudinal bundles of fibrous sheath. 



sheath are columnar and placed vertically upon the glassy mem- 

 brane, while the cells of the succeeding layers, some five to ten 

 deep, present the polygonal outlines and the intercellular connect- 

 ing threads seen in the corresponding parts of the ordinary epider- 

 mis. The space between the outer root-sheath and the hair is occu- 

 pied by three narrow zones, which collectively form the inner 

 root-sheath, a clear transparent rigid membrane closely embracing 

 the lower two-thirds of the hair-follicle and terminating in the vicinity 

 of the opening of the sebaceous gland. The outer or Henle 's 

 layer appears as a light band composed of somewhat elongated 



