STRUCTURE OF THE HAIR. 251 



hair follicle into epidermic scales that, arranged in several 

 layers, cover the external root-sheath, which is also composed 

 of flattened cells. In many cases, however, it occurs that this 

 sheath constitutes an investing membrane to the hair through- 

 out the neck of the hair follicle and the excretory passage ; 

 though in most cases its composite scales coalesce with the 

 epidermic scales of this passage. 



The topographical arrangement of the different sheaths can 

 only be thoroughly investigated in successful longitudinal 

 sections. Thick and grey hairs are best adapted for exami- 

 nation, since they can be easily divided longitudinally, and 

 because the want of pigment permits the various cells of the 

 hair substance to be distinctly seen. Preparations made with 

 needles and transverse sections then complete the picture. 



As the papillae of the hair are situated at different depths, 

 no two present the same appearances, although the section 

 may have been carried quite parallel to the surface. The 

 appearances vary in fact with the height at which the hair 

 has been divided! Sometimes a papilla composed of connec- 

 tive tissue will be seen invested by several layers of epithelium- 

 like cells, that are again enclosed by the vitreous membrane; 

 this is a transversfe section of the neck of the papilla. It is 

 bounded by the cells of the hair root, in which neither the 

 cuticle nor the sheath of Huxley can be differentiated. The 

 external root-sheath is as yet absent. 



In other instances, again, the medulla of the hair, composed 

 of oblong quadrangular cells, may be seen to occupy the axis 

 of the cortex, which consists of nucleated polyhedric cells. The 

 cortex is bounded by several concentrically arranged fine lines, 

 between which are delicate oblong nuclei (cuticle of the hair 

 and of the root). External to these is a layer composed of a 

 double row of cells, which contain, not only many bright 

 granules, but also distinct nuclei (Huxley's sheath), enclosed 

 by a single series of highly refractile, hemispherical, non- 

 nucleated cells, that do not stain with carmine (internal root- 

 sheath of Henle), forming a layer that is again invested by the 

 epithelial cells in contact with the vitreous membrane (external 

 root-sheath). 



The section here has been carried through the still soft root 



