156 THE SKIN. 



pili muscles, which elevate the hairs and cause projections of the 

 skin at their bases (cutis anserina). The hair-follicles consist 

 of two parts an outer fibrous sheath derived from the coriuni, 

 and an inner epithelial portion continuous with the epidermis. 



The outer fibrous sheath is a supporting investment of fibrous 

 tissue, longitudinally and circularly arranged, continuous with 

 the coriuni ; its innermost layer, next to the epidermic sheath, 

 is a translucent basement-membrane, the hyaline layer. At 

 the lower end of the follicle the corial tissue sends a cellular 

 and vascular projection, the papilla, into the hair-bulb. 



The inner and more conspicuous epithelial portion of the 

 hair-follicle is formed by a dipping clown of the epidermis 

 about the root of the hair. It corresponds mainly to the rete 

 mucosum, the stratum corneum extending inward only a short 

 distance near the mouth of the follicle. The epidermic por- 

 tion of the follicle is usually described as consisting of two 

 parts, an outer root- sheath and an inner root-sheath. 



The outer root-sheath is a continuation of the stratum Mal- 

 pighii, and consists of several layers of cells similar to those 

 of that layer in the epidermis. The outermost layer of col- 

 umnar cells, resting on the hyaline membrane, is very well 

 marked. Alongside the expansion of the bulb of the hair 

 the outer or Malpighian sheath becomes thinner. At the 

 lower portion of the bulb this sheath curves around, upward, 

 and inward, resting on the papilla, and becomes continuous 

 with the cells of which the hair is composed, which are thus 

 formed by gradual transition from the Malpighian cells ; the 

 innermost cells in this situation, next the papilla, become 

 cuboidal and merge into the medulla of the hair, while the 

 outer cells become gradually converted into the elongated 

 horny cells of the hair-cortex. 



The inner root-sheath lies between the hair and outer sheath 

 along the lower half of the follicle ; above it changes to a 

 homogeneous sheath which fades gradually away, while be- 

 low, in the lower part of the bulb, the inner sheath is gradu- 

 ally lost. It consists of three layers Henle's layer, Hux- 

 ley's layer, and the cuticular layer, from without inward. 



The layer of Henle is a thin, translucent stratum composed 

 of a single layer of flattened cells, next to the Malpighian 

 sheath. Next within is the layer of Huxley, consisting of 



