DEVELOPMENT OF HAIRS. 



Cells are deposited outside the limitary membrane, which eventually give rise to 

 fibres, corpuscles, and other constituents of the dermic coat. While this is going on 

 outside, the cells within the follicle undergo changes. Those in the middle lengthen 

 out conformably with the axis of the follicle, and give rise to the appearance of a 

 short conical miniature hair, faintly distinguishable by difference of shade from the 

 surrounding mass of cells, which are also slightly elongated, but across the direction 

 of the follicle. The papilla (figs, cxviu., &c., h) makes its appearance at the swollen 

 root of the little hair ; and the residuary cells contained within the rudimentary 

 follicle form the root-sheath, the inner layer of which, or inner root-sheath, lying 

 next to the hair (fig. cxix., d), is soon distinguished by its translucency from the more 

 opaque outer part that fills up the rest of the cavity. The young hair continuing to 

 grow, at last perforates the cuticle (fig. cxx., g), either directly, or after first slanting 

 up for some way between the mucous and horny strata. The young hair is often bent 

 like a whip, and then the double part protrudes. 



Fig. CXVIII. 



Fig. CXIX. 



Fig. CXVIII. RUDIMENT OF A HAIR OF THE EYEBROW, MAGNIFIED 50 DIAMETERS 

 (after Kolliker). 



The cells form an internal cone indicating the position of the future ^ hair, a, horny 

 layer of cuticle ; 6, mucous layer ; c, external layer of root-sheath ; i, limitary membrane ; 

 ~h, papilla. 



Fig. CXIX. HAIR-RUDIMENT MEASURING 0'22 OF A LINE, FROM THE EYEBROW, WITH 

 THE YOUNG HAIR NOT YET RISEN THROUGH THE CUTICLE (after Kolliker). 



a, 6, c, h, i, as in fig. cxviu. ; e, hair-knob ; /, stem, and g t point of the hair ; d, 

 internal layer of the root-sheatb, still inclosing the hair ; n, n, commencing sebaceous 

 follicles. 



Fig. CXX. HAIR-FOLLICLE FROM THE EYEBROW WITH THE HAIR JUST ERUPTED ; THE 

 INNER LAYER OF THE ROOT-SHEATH RISES TO THE MOUTH OF THE HAIR-FOLLICLE 

 (after Kolliker.) 



The letters denote the same parts as in Fig. CXIX. 



The first hairs produced constitute the lanurjo ; their eruption takes place about 

 the fifth month of intra-uterine life, but part of them are shed before birth, and are 

 found floating in the liquor amnii. Kolliker affirms that the infantile hairs are 

 entirely shed and renewed within a few months after birth ; those of the general sur- 



P 



