SECT. 64.] HAIRS. I 1 5 



its colls individually more or less projecting. Thence upwards, its 

 place is occupied by the external root-sheath, the innermost cells 

 of which soon assume all the characters of those of the horny 

 layer of the epidermis. 



The cuticle of the inner root-sheath is closely applied to the 

 interior of the root-sheath in its whole extent, and resembles very 

 much the cuticle of the hair itself, which it immediately adjoins. 

 It becomes especially distinct on the addition of caustic potash or 

 soda, frequently detaches itself on pressure from the hairs, along 

 with the inner root-sheath ; while the cuticle of the hair, thrown 

 into undulating creases, remains lying upon the fibrous substance, 

 and in this condition can be studied with facility, both in a profile 

 and superficial view. In torn-out hairs, this layer is ouly found 

 when they are still covered by the inner root-sheath, otherwise it 

 remains behind in the hair-follicle. It consists of non-nucleated, 

 i lubricated, broad cells, which never swell up, and which dissolve 

 with difficulty in alkalies ; they are, however, thicker than those of 

 the cuticle of the hair, and measure in the longitudinal direction of 

 the hair only o - oo2'" to o # oo4'". The whole of this layer measures 

 o - ooi 6'" to o - oo2'", and is continued, at the hair-bulb, with a 

 tolerably distinct line of demarcation, into large nucleated cells, 

 disposed in the same manner as those into which the cuticle of the 

 hair itself passes, except that they are generally smaller. 



I regard, with lieichert, the outer root-sheath as the epidermis of the fol- 

 licle, and the inner, together with its cuticle, as an independent layer belong- 

 ing to the hair ; only I cannot admit, as Rciehert seems to do, that the inner 

 root-sheath, with its cuticle, continues to grow in the developed hair. 



§ 64. Development of the Hairs. — The first rudiments of the 

 hairs are flask-shaped, solid processes, entirely composed of cells, 

 formed by the growth inwards of the mucous layer of the epidermis, 

 in which the inner and outer cells become modified in such a way 

 that the former are converted, first, into a small delicate hair in 

 the axis of the rudiment, and, secondly, into an internal sheath 

 surrounding this (both being transformed into a horny substance) ; 

 while the latter remain more unaltered and soft, and appear as the 

 external sheath and soft cells of the hair-bulb. The hairs and 

 sheaths, therefore, arc developed at once in their totality ; the 

 former as miniature hairs, with root, shaft, and point. Thus the 

 point is not first formed, as is the case with the crow r n of the teeth, 

 and still less can it be said that the hair begins with the root, as 

 has been sometimes supposed. The elements of the youngest 



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