Chap, xxxiv.] THE SKIN. 285 



teiice, for its hair-follicle, including the papilla, sooner 

 or later undergoes degeneration, and subsequent to 

 this a new papilla and a new hair are formed in its 

 place. What happens is this the lower part of 

 the hair-follicle, including the papilla and hair-bulb, 

 degenerates and is gradually absorbed. Then there 

 is left only the upper part of the follicle, and in 

 the centre of this is the remainder i.e.j non-degene- 

 rated portion of the hair root. The fibres of this are 

 at the extremity fringed out and lost amongst the 

 cells of the outer root-sheath of the follicle. This 

 represents the hair-knob (Henle). Now, from the 

 outer root-sheath a cylindrical outgrowth of epithe- 

 lial cells into the depth takes place ; against the 

 extremity of this a new papilla is made. In con- 

 nection with this new papilla, and in the centre of 

 that cylindrical outgrowth, a new hair and hair-bulb 

 are formed, and as these gradually grow outwards 

 towards the surface they lift, or rather push, the old 

 hair i.e., the hair- knob out of the follicle. The 

 ^outer part of the follicle of the old hair persists. 



Thus we find in all parts of the skin where hairs 

 occur, complete or papillary hairs side by side with 

 degenerating hairs, or hair-knobs. 



388. Development of hair. In the human 

 foetus the hair-follicles make their first appearance about 

 the end of the third month, as solid cylindrical out- 

 growths from the stratum Malpighii. This is the rudi- 

 ment of the outer root-sheath. After having pene- 

 trated a short distance into the corium, this latter be- 

 comes condensed around it as the rudiment of the hair- 

 sac, and at the distal extremity forms the papilla 

 growing against the outer root-sheath and inva- 

 ginating it. In connection with the papilla a rapid 

 multiplication of the epithelial cells of this extremity 

 of the outer root-sheath takes place, and this forms the 

 j by the multiplication of whose cells the hair 



