HAIRS. 327 



sheath. They are undifferen dated, and do not yet show the 

 characteristics by which the cells of these individual layers are 

 distinguished. The matrix cells of all layers are cylindrical 

 or polygonal cells, rich in protoplasm. All the sheaths do not 

 show a cornification at the same level, and the keratohyaline 

 granules or eleidin droplets cannot be recognized in all of 

 them. ' The cortical substance and cuticula pili become corneous 

 without the presence of keratohyaline granules, while in the 

 medullary substance there can usually be recognized droplets of 

 keratohyaline. We find this substance in all three layers of the 

 inner root sheath (Fig. 246). In the deeper parts the granules 

 are present in Henle's sheath. Farther toward the surface they 

 are more abundant, until finally we come to cells with rudi- 

 mentary nuclei and corneous contents. We thus see that in 

 the inner root sheath the growth as well as the process of 

 cornification takes place from below upward to the surface 

 of the skin. 



The bulb of the hair which is about to fall out becomes 

 corneous, separates from the papilla, and splits up into many 

 fibres. Such a dying hair loses its connection with the papilla 

 in consequence of an increase in the cells of the root sheaths. 

 The root sheaths, being empty, form between the papilla and 

 the lower thickening of the dead hair a cord-like mass of cells 

 (Fig. 249). In place of such a hair there appears a new hair, 

 formed by a multiplication of epithelial cells. This rests on 

 the papilla and grows upward until the first hair is forced 

 out. 



In connection with hairs, we must speak of the bundles 

 of smooth muscle cells making up the so-called arrectores 

 pilorum, since these are connected directly with the hair follicle. 

 These bundles have their origin in the stratum papillare of the 

 corium, and are inserted at the lower part of the hair follicle. 

 The hairs are inserted always in the skin at an angle to the 

 surface. On the side where the hair follicle forms an obtuse 

 angle with the skin surface there is fastened a bundle of 

 smooth muscle fibres. The contraction of these fibres causes 

 an erection of the hair. The simultaneous formation of a de- 



