OF THE HAIRS. 



189 



out, never exist, and the supposition that they do, rests upon a wholly 

 subjective foundation. 



Fig. 75. 



Fig. 74. 



The downy hairs, lanugo, the eruption of which is completed in the 

 23-25th week, are short fine hairs, whose peculiar arrangement has been 

 noted above. They measure on the bulb 0-01, on the shaft 0-006, at 

 the point 0-0012-0-002 of a line; are pale, or almost .colorless, and 

 consist only of cortical substance and a cuticle. In man, the bulb is 

 usually colorless, and often rests upon a very distinct papilla, arising 

 in the ordinary manner from the bottom of the hair-sac. It has the 

 same three layers as in the adult, and possesses a very well-developed 

 epidermic investment, consisting of an external root-sheath of 0-004- 

 0*012, and an inner sheath of 0-006-0-008 of a line, without openings. 



After their eruption, the downy hairs grow slowly to a length of J J 

 of a line, and in fact to a greater length in the head than elsewhere. 

 Generally they remain to the end of foetal life, gradually acquiring a 

 darker color, becoming in many cases, as on the head, even blackish ; 

 another small portion falls off into the liquor amnii, is swallowed with 



FIG. 74. Rudiment of a hair from the eyebrow (0-22 of a line in length), its inner cells 

 forming a distinct cone, as yet without any hair, but with the papilla indicated: a, horny 

 layer of the epidermis; 6, mucous layer; c, outer root-sheath of the subsequent sac; i, struc- 

 tureless membrane upon its outer side ; /, papilla of the hair. Magnified 50 diameters. 



FIG. 75. A, rudimental hair from the eyebrows, with just developed but not yet erupted 

 hair, of O28 of a line in length. The inner root-sheath projects beyond the point of the hair 

 somewhat at the upper part, and laterally at the neck of the sac; the first rudiments of the 

 sebaceous glands appear in the form of two papillary outgrowths from the outer root-sheath. 

 .B, hair-sac from the same, with its hair just erupted ; the inner root-sheath projects through 

 the aperture of the hair-sac; the rudiments of sebaceous glands are as yet not developed; 

 o. 6, c, /;. t, have the same signification as in Fig. 74 : e, hair-bulb; /, hair shaft; g, hair-point; 

 ft, rudiments of the sebaceous glands. 



