224 



THE SKIN. 



Development of hair in the foetus. — The radiments of the hau'S 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. 151), filled with cells of precisely the same nature as those of 

 the Malpighian or mucous layer of the cuticle, Avith 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. 152). Cells are deposited outside the limitary 

 membrane, which eventually give rise to fibres, corpuscles, and other constituents 



Fig. 152, — A. Rudiment op a Hair of the Eyebrow, jiagnified 50 Diameters 



(KolUker). 



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

 layer of cuticle ; &, mucous layer ; c, external layer of root-sheath ; /, limitary membrane ; 

 A, papilla. 



B. — Hair-Rudiment from the Eyebrow, with the Young Hair not yet risen 



THROUGH THE CuTICLE. 



f, hair-knob ; /, stem, and g, jjoint of the hair ; d, internal layer of the root-sheath, 

 still inclosing the hair ; n, n, commencing sebaceous follicles. 



C. — Hair-Follicle from the Eyebrow with the Hair just Protruded ; the Inner 

 Layer of the Root-Sheath rises to the Mouth of the Haiu-Follicle. 



of the dermic coat. "While this is going on outside, the cells within the foUicle 

 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 (fig. 152, h) makes its appearance at the swollen root of the 

 little hair ; and the residuary cells contained within the nidimentaiy follicle 

 foim the root-sheath, the inner layer of which, or inner root-sheath, lying nexfc 



