u6 



HAIRS. 



[sect. 64. 



hairs are nothing but elongated cells, similar to those of the fibrous 

 substance of the subsequent hairs, which arise by the lengthening 

 and chemical metamorphosis of the innermost cells of the hair- 

 rudiments. Medullary cells are wholly absent ; on the other hand, 

 the cuticle is very obvious. The inner sheath is striated, exhibits 

 no gaps, and consists of elongated cells, which have been developed 

 from the cells situated between the hair and the outer sheath. 

 The proper hair-follicle, as regards its fibrous layers, is formed in 

 loco from the formative cells of the cutis, which surround the hair- 

 rudiment. It may, however, be conceived as an inversion of the 

 cutis, connected with the inward growth of the processes of the 

 epidermis. Its structureless membrane, which appears so early, 

 may be closely related to the external cells of the hair-rudiment, 

 which correspond to the outer root-sheath, and, like the membranse 

 propriae, may be formed by an excretion from them. As to the 

 hair-papilla, we cannot but regard it as a growth of the fibrous 

 part of the hair-follicle, analogous to the papillse of the corium in 

 general. 



The first rudiments of the downy hairs, and of their sheaths, are found in 

 Fig. 51. the human embryo at the end of the 



third or the commencement of the 

 fourth month, on the forehead and 

 eyebrows ; they consist of papilliform 

 collections of cells, 0*02'" in diameter 

 (fig. 51). In the fifteenth week the 

 processes are larger (0-025'" to o'os'" 

 long, b'oii" to o - o2"' broad), flask- 

 shaped, and surrounded by a delicate 

 covering, which is continuous with a 



Hair-rudiments, from the forehead of a human delicate membrane between the rete 

 embryo, sixteen, weeks old; magnified 380 times. MalpiqHi and cutis, but more inti- 

 n Hornv layer of the epidermis ; A. mucous layer x ■' 



mately united with the former. 



Besides this covering, which is, in- 

 deed, nothing but the structureless 

 membrane discovered by me in the 

 fully-developed hair-follicles, another and more exterior layer of cells occurs 

 on the hair-follicles, which generally comes away with them from the cutis in . 

 shreds, rarely entire. I look upon this as the first indication of the fibrous 

 layers of the hair-follicles. In the sixteenth and seventeenth weeks, the pro- 

 cesses of the mucous layer, which I shall henceforth simply call hair-rudiments, 

 enlarge up to 0-04'" to o - o6'" in length, and 0-03'" to 0-04'" in breadth, and their 

 coverings become thicker, although they do not present as yet the least trace 

 of a hair. In the eighteenth week, the first indications of the hairs are seen 

 in the eyebrows, in hair-rudiments of o - i"' and 0-2!" , their central cells being 

 lengthened, and their long axis disposed parallel to that of the rudiment ; 

 whilst the peripheral cells are arranged with their long diameter transversely. 



a 



/CP,'-Wo^;: .r- : ,:-.■ 



of the same ; i. structureless membrane surround' 

 ino- the hair-rudiment, and continued between the 

 mucous layer and the corium ; m. rounded, in 

 part elongated cells, of which the hair-rudiment 

 is principally composed. 



