136 



THE ESSENTIALS OF HISTOLOGY. 



the minute hair grows, it pushes its way through the layers of the 

 epidermis, which it finally perforates, the epitrichial layer being thrown 

 off (p. 129). The hair-rudiments commence at the third or fourth 

 month of fostal life ; their growth is completed about the fifth or sixth 

 month, and they form a complete hairy covering termed the lanugo. 



FIG. 160. HAIR-RUDIMENT FROM AN 

 EMBRYO OF six WEEKS. (Kolliker.) 

 a, horny, and 6, mucous or Malpighian 

 layer of cuticle ; i, basement-mem- 

 brane ; in, cells, some of which are 

 assuming an oblong figure, which 

 chiefly form the future hair. 



FIG. 161. DEVELOPING HAIR FROM 



HUMAN EMBRYO OF 4i MONTHS. 



(Ranvier.) 



p, papilla ; /, hair-rudiment ; i, cells 

 forming inner root-sheath ; k, kera- 

 tinised part of inner root-sheath, 

 uncoloured by carmine ; e, outer 

 root-sheath ; b, epithelial projection 

 for insertion of arrector pili ; s, 

 sebaceotis gland ; t, sebaceous 

 matter forming independently in 

 the part which will become the 

 neck of the follicle. 



This is entirely shed within a few months of birth, the new hairs being 

 formed in downgrowths from the old hair-follicles in the manner already 

 mentioned. 



Hairs grow at the rate of half an inch per month. They are found 

 all over the body except on the palms of the hands and the soles of the 

 feet, and on the distal phalanges of the fingers and toes. They usually 



