DEVELOPMENT OF THE HAIR. 255 



However variable the length and thickness of the hairs may 

 be the above-described constituents are always present. 



The different colours presented by the hair depend chiefly 

 on the pigment contained in the hair cells, that either exists in 

 the form of granules, or is equably diffused. But the colour of 

 the hair also depends on small bubbles of air that either occur 

 between the cortical scales and the medullary cells, or are found 

 in their interior. Langerhans maintains that the papillae are sur- 

 rounded by a considerable number of double-contoured nerve 

 fibres. In specimens prepared with chloride of gold it may be 

 demonstrated that varicose fibres belonging to the non-medul- 

 lated nerve fibres which accompany the bloodvessels into the 

 papilla, extend from the bulb between the cells of the hair root, 

 and run parallel to the papilla to its apex. 



DEVELOPMENT AND SUCCESSION OF THE HAIR. 



The first rudiment of the hair follicle and of the external 

 root-sheath, in the human embryo, occurs at the end of the 

 third or the beginning of the fourth month as a club-shaped 

 depression of the surface of the corium, into which the cells of 

 the mucous layer are prolonged, and which they completely 

 occupy. 



A finger-shaped column is thus formed from cells of the 

 rete mucosum, which is as yet destitute of a special investing 

 membrane, being only surrounded by the connective-tissue 

 fibres of the corium. 



A further rudiment of the hair is formed at the bottom of 

 this process as a short column half its thickness, and, like it, 

 composed of cells. 



Between these cells, that may be distinguished from those of 

 the before-mentioned process by their large nuclei and small 

 amount of surrounding protoplasm, bloodvessels soon make 

 their appearance, and the smaller column is then recognizable 

 as the rudiment of the hair papilla, which in lanuginous hairs 

 is characterized by the abundance of its cells. 



Around the papilla that has thus been formed small round 

 cells soon accumulate, causing the hair follicle to deepen, and 

 making a cavity for themselves in the column formed by the 



