THE SKIN. 565 



The explanation of the diagram is as follows : The epidermis, bulging 

 downward, results in the formation of the inner root-sheath, while the rete 

 mueosum, prolonged downward, forms the outer root-sheath. 



The bundles of the connective tissue of the derma, which give an outer 

 investment to the pouch, composed of both root-sheaths, produce the follicle. 

 Its innermost portion exhibits cross-sections of smooth muscle-fibers. 



The papilla of the hair is a product of the follicle. Around the papilla is a 

 knob the bulb of the root of the hair which continues into the root of the 

 hair that part inclosed in the pouch; and the shaft of the hair that part 

 standing forth on the surface of the skin. 



The diagram shows that the inner root-sheath, upon approaching the 

 bottom of the pouch, becomes widened, and at the bottom of the pouch turns 

 over, thus first producing the bulb, afterward the root, and the shaft of the 

 hair itself. The innermost layer of the inner root-sheath, by turning over, 

 results in the formation of the cuticle, the single investing layer of both the 

 root and the shaft of the hair. 



The figure demonstrates, furthermore, that the outer root-sheath, upon 

 approaching the bottom of the pouch, becomes thinner, and perishes at last, 

 while on one side the outer root-sheath produces the pouch of the sebaceous 

 gland. Between the outer root-sheath and the follicle there is a homogeneous 

 layer the so-called structureless membrane. The arrector pili muscle is in 

 connection with the muscle-layer of the follicle and surrounds the bottom of 

 the sebaceous gland. 



Our diagram serves as a key, which enables us to comprehend 

 easily all formations of the skin engaged in the construction of 

 the hair. (See Fig. 235.) The pouch, as a rule, has a funnel- 

 shaped widening on the surface of the skin, which is covered by 

 stratified epidermal scales. These scales are traceable in direct 

 union with the inner root-sheath, which begins on the so-called 

 neck of the pouch, being composed of two epidermal layers only, 

 and, in honor of the discoverer, termed Henle's sheath. Next to 

 the inner root- sheath lies the extremely delicate cuticle of the 

 hair, which ensheathes both the root and the shaft of the hair. 

 With higher powers we see on each hair finely serrated edges 

 the slightly bulging edges of the cuticle. The hair is com- 

 posed of closely packed, horny epidermal spindles, which hold a 

 varying amount of pigment granules. The rete mueosum elon- 

 gates directly into the outer root-sheath, and this into the seba- 

 ceous gland. It is only the duct of this gland which is covered 

 by flat, horny epithelia, while the gland, as such, is composed of 

 cuboidal epithelia, like any acinous gland. The duct of the seba- 

 ceous gland, as a rule, empties into the funnel-shaped widening 

 of the pouch, in the space between the inner root-sheath and the 

 hair, or, more particularly, its covering cuticle. The outer root- 

 sheath is composed of several strata of epithelia, like the rete 



