I 



THE SKIN. 567 



directly connected with the adjacent columnar epithelia by very 

 marked prickles and thorns. To the presence of these thorns D. 

 Haight first drew attention. 



The pouch of the sebaceous gland is under the control of 

 the arredor pili muscle, which represents a flat, fan-like sheet, 

 whose broad ends terminate in the papillary layer, while the nar- 

 row end is inserted in the follicle of the root of the hair. No 

 doubt, the evacuation of the sebaceous gland is done by contrac- 

 tion of this muscle-sheet. The fatty mass will be squeezed first 

 into the funnel of the hair-pouch, as a rule, and only from large 

 sebaceous glands directly to the surface. 



The lower extremity of the hair-pouch, in specimens taken 

 from the human skin, is readily understood if we have made a 

 study of the hair of animals, especially of those strong hairs on 

 the upper lip of kittens. It is, perhaps, for this reason that, after 

 many years' busy writing, not one author has given a plain 

 description of the relations. As a matter of course, the essentials 

 are identical in the hair of kittens and that of man, though the 

 former are, as a rule, plainer than the latter. (See Fig. 236.) 



The inner root-sheath in its upper portion shows the light, 

 horny Henle's layer. In an oblique line there appear polyhedral 

 epithelia; in the upper portions pale and finely granular, with 

 indistinct nuclei ; deeper down, coarsely granular and slightly 

 elongated. This latter part of the inner root-sheath represents 

 what has been termed Huxley's layer. It is seen that at the bot- 

 tom of the pouch this layer turns over, surrounds the papilla, 

 and constitutes the bulb of the root of the hair. The epithelia 

 on the lower periphery of the papilla are columnar, gradually 

 changing into the cuboidal form, and farther up become elon- 

 gated, spindle-shaped. Lastly, they emerge into the horny 

 spindles which produce the main bulk of the hair. The bound- 

 ary line between the inner root-sheath and the root of the hair 

 is produced by a thin, apparently structureless, layer, outside 

 of which is the inner root- sheath, inside the cuticle of the hair. 

 The cuticle on the upper portion of the root is composed, as well 

 as on the shaft, of thin, imbricated scales, whose edges are slightly 

 elevated above the surface of the hair, and give the latter the 

 peculiar serrated appearance. Gradually, the epithelia of the 

 cuticle of the root assume a columnar shape and become nucleated. 

 At the height of the bulb these columnar epithelia are very large, 

 pale granular, and supplied with large and distinct nuclei. 

 Their characteristic row runs in the middle, between Huxley's 



