290 MANUAL OF HISTOLOGY. 



The hair-follicles and hairs stand obliquely to the surface 

 of the skin. Their direction varies in different regions of the 

 body, and depends upon the structure of the connective tissue 

 of the corium and the degree of its tension. The contents of 

 the hair-follicles are the external and internal root-sheaths and 

 the hair proper. 



The external root-sheath (f) adjoins the inner follicle sheath 

 and consists of rete cells continued into the hair-follicle from 

 the general rete mucosum layer of the skin. This sheath does 

 not extend as far as the lowest part of the follicle, generally 

 ending about on a level with the apex of the hair-papilla, 

 though it is sometimes continued as far as the base of the 

 latter. All the different kinds of cells present in the epi- 

 dermis are also found in this sheath as far down as the neck 

 of the follicle. Beyond this point the cells of the rete Mal- 

 pighii only enter into its formation. The number of rows of 

 cells forming it is subject to great variation. It diminishes 

 as the base Of the follicle is approached, so that finally the 

 sheath is formed of a single row of cells. At the neck of 

 the follicle the sheath is usually narrower than directly above 

 or below this point, owing to the pressure to which the cells 

 are here subjected. Their form is very similar to that of 

 the corresponding cells of the rete mucosum. Those of the 

 deepest row are cylindrical, and those of the second row 

 polyhedral. In the other rows the cells are flatter, with the 

 exception of the most internal row, where all these bodies 

 are large and round. This last row is not subject to the same 

 changes as the others, and has been considered to be a distinct, 

 independent row of cells (Unna). The nuclei of all the cells 

 color strongly in carmine, hsematoxylon, etc. Nerve-fibres have 

 been described as running between the cells of this sheath 

 (Langerhans). 



The internal root-sheath (g) lies in direct contact with the 

 external root-sheath. It is usually described as consisting of 

 two layers, an external one, also called the slieatJi of Henle, 

 and an internal one, or sheath of Huxley. Strictly speak- 

 ing, this division into two sheaths is incorrect, as it has been 

 shown (Unna) that the two sheaths supposed to be distinct 

 ,have a common origin from the cylindrical epithelial cells sur- 

 'rounding the neck of the hair-papilla at its lowest part. These 

 cells color very deeply in carmine. They surround the root of 



