256 SKIN, HAIR, AND NAILS, BY ALFRED BIESIADECKI. 



mucous layer. As these cells become converted into long 

 spindles, they penetrate further and further into the column of 

 the mucous layer, pressing it outwards in all directions, so that 

 the cells of which it is composed come to constitute the cells of 

 the external root-sheath. 



The cells surrounding the papilla form the root of the hair, 

 and from them both the hair itself and the sheath of Huxley 

 are developed. Those in immediate proximity to the papilla 

 remain soft, but at the point where they are already contained 

 in the external root-sheath they soon become horny. This has 

 led several observers to maintain that the apex of the hair is 

 first formed, and that the root is developed subsequently ; on 

 the contrary, others have adopted the view that the axial cells 

 of the column formed by the mucous layer become converted 

 into the cells of the hair proper. 



The peripheric cells of the root of the hair become the scales 

 of Huxley's sheath, which also invests the apex of the hair. 

 Both remain for some time within the external root-sheath, 

 bounded above by the cells of the mucous layer, but gradually 

 both the latter and the epidermis, as well as the external 

 sheath, are perforated by the growing hair, and the point of 

 the hair enclosed by Huxley's sheath comes into view. Finally, 

 the hair appears to grow more rapidly than the sheath of 

 Huxley, which at length it also penetrates. 



The development of the hair follicle has not been accurately 

 studied. 



The first rudiments of the hair do not make their appearance 

 simultaneously in all parts of the body; and it would also 

 appear that the time required for their development up to the 

 period of eruption, is different in different parts of the body. 

 The first to appear are those of the eyebrow and eyelashes, 

 then those of the head, and subsequently those of the rest of 

 the body. Nearly all the hairs project beyond the surface of 

 the body at the twenty-fourth week. 



Hairs of embryoes developed in this manner are always lanu- 

 ginous ; i.e., are very minute, with short hair follicles. In 

 many regions the lanuginous hairs are permanent; but in others 

 thick hairs are subsequently developed, by which they are 

 replaced. 



