STRUCTURE OF THE HAIR. 245 



with the internal sheath of the follicle, is smooth ; whilst its 

 inner surface exhibits delicate transverse ribs or prickles, re- 

 sembling those of the prickle cells (Haight) .* 



The vitreous layer is a continuation of the basement membrane 

 covering the surface of the corium ; it lines the internal sheath 

 of the hair follicle, extending as far as the neck of the papilla, 

 and becoming gradually thinner before it ceases. It would 

 appear, however, that, reduced to an extremely thin lamina, it 

 covers the body and even the apex of the papilla. 



Neither bloodvessels nor nerves are to be found in the 

 vitreous layer. 



The root-sheaths (/) that we have already alluded to as ad- 

 ditional constituents of the hair follicle, consist of two layers, 

 the outer and the inner root-sheaths. 



The external root-sheath (/), is formed by the rete mucosom 

 that is continued into the hair follicle from the surface of the 

 skin, but does not extend as far as the bulb, terminating usually 

 at the level of the apex of the papilla, or in many cases even 

 above it (Moleschott, Chapuis). It consists of several layers 

 of epithelial cells, of which those in contact with the vitreous 

 membrane are usually columnar, and exhibit a nucleus situated 

 in that part which is most distant from this membrane. 



The cells succeeding to this internally are polyhedral, whilst 

 the innermost are flattened, and include an oval nucleus. 



In the neck of the hair follicle the external root-sheath is 

 thinner than elsewhere, chiefly in consequence of the several 

 layers of cells of which it is composed presenting a more 

 flattened form. Towards the hair bulb the layer terminates 

 generally in a rounded manner, presenting a triple tier of cells, 

 but sometimes more pointedly by becoming reduced to only a 

 single row of flat cells. In specimens prepared with chloride of 

 gold, fine varicose dark-violet fibres may be found here and 

 there between the cells of the external root-sheath, which pro- 

 ceed from the vitreous membrane, and extend as far as to the 

 inner root-sheath. The probability that these are nerve fibres 

 has not up to the present time been supported by any proof 

 that they are continuous with the nerve fibres distributed to 



* Sitzungsberichte der Akademie in Wien, 1868, Band Ivii. 



