ccxii HAIRS. 



the fibrous part of the hair, and certain of them, previously getting filled 

 with pigment, give rise to the coloured streaks and patches in that tissue ; 

 their nuclei, at first, also lengthen in the same manner, but, at last, partly 

 become indistinct. The cells next the circumference expand into the scales 

 which form the imbricated cuticular layer (fig. cxv., e, e). The medulla, 

 where it exists, is formed by the cells nearest the centre ; these retain their 

 primitive figure longer than the rest ; they become coherent, and their 

 cavities may coalesce together by destruction of their mutually adherent 

 parietes, whilst collections of pigment granules make their appearance in 

 them and around their nuclei, forming an opaque mass, which occupies the 

 axis of the hair. 



Fig. CXVII. 



Fig. CXVL SECTION OF THE SKIN OF THE HEAT>, WITH TWO HAIR FOLLICLES, 

 SLIGHTLY MAGNIFIED (from Kblliker). 



a, epidermis ; b, corium ; c, muscles of the hair-follicles. 



Fig. CXVII. HAIR RUDIMENT FROM AN EMBRYO OF Six WEEKS, MAGNIFIED 350 

 DIAMETERS (after Kolliker). 



a, horny, and 6, mucous or Malpigbian layer of cuticle ; i, 1'mitary membrane ; m, cells 

 some of which are assuming an oblong figure, which chiefly form the future hair. 



The substance of the hair, of epidermic nature, is, like the epidermis 

 itself, quite extravascular, but, like that structure also, it is organised and 

 subject to internal organic changes. Thus, in the progress of its growth, 

 the cells change their figure, and acquire greater consistency. In conse- 

 quence of their elongation, the hair, bulbous at the commencement, becomes 

 reduced in diameter and cylindrical above. But it cannot be said to what 

 precise distance from the root organic changes may extend. Some have 

 imagined that the hairs are slowly permeated by a fluid, from the root to 

 the point, but this has not been proved. The sudden change of the colour 

 of the hair from dark to grey, which sometimes happens, has never been 

 satisfactorily explained. 



Development of the hair in the foetus. The rudiments of the hairs may be dis- 

 cerned at the end of the third or beginning of the fourth month of intra-uterine life, 

 as little black specks beneath the cuticle. They at first appear as little pits in the 

 corium (fig. cxvu.), filled with cells of precisely the same nature as those of the 

 Malpighian or mucous layer of the cuticle, with which they are continuous; so it 

 might correctly be said that the hair-rudiments are formed of down growths of 

 the mucous layer, which sink into the corium. A homogeneous limiting membrane 

 next appears (?'), inclosing the collection of cells, and continuous above with a similar 

 simple film which at this time lies between the cuticle and the corium; it becomes 

 the innermost or hyaline layer of the dermic coat of the follicle. The hair-rudiments 

 next lengthen and swell out at the bottom, so as to assume a flask -shape (fig. cxvin.). 



