THE SKIN AND ITS APPENDAGES. 



1H1 



FIG. 682. Transverse section 

 of hair-follicle. 1. Dermic coat 

 of follicle. 2. Epidermic coat or 

 root-sheath, a, Outer layer of 

 derniic coat, with blood-vessels. 

 6,6. Vessels cut across, c. Middle 

 layer, d. Inner or hyaline layer. 

 (. Outer root-sheath. /. g. Inner 

 root-sheath, h. Cuticle of root- 

 sheath, i. Hair. (From Quain's 

 Anatomy, Biesiadecki.) 



of considerable length the follicle extends into the subcutaneous cellular tissue. 

 The hair-follicle commences on the surface of the skin with a funnel-shaped open- 

 ing, and passes inward in an oblique or curved direction the latter in curly hair- 

 to become dilated at its deep extremity, where it cor- 

 responds with the bulbous condition of the hair which 

 it contains. It has opening into it, near its free ex- 

 tremity, the orifices of the ducts of one or more seba- 

 ceous glands. At the bottom of each hair-follicle is a 

 small conical, vascular eminence or papilla, similar in 

 every respect to those found upon the surface of the 

 skin ; it is continuous with the dermic layer of the fol- 

 licle, is highly vascular, and probably supplied with 

 nervous fibrils. In structure the hair-follicle consists 

 of two coats an outer or dermic, and an inner or 

 epidermic. 



The outer or dermic coat is formed mainly of fibrous 

 tissue-; it is continuous with the corium, is highly 

 vascular, and supplied by numerous minute nervous 

 filaments. It consists of three layers (Fig. 682). The 

 most internal, next the cuticular lining of the follicle, 

 consists of a hyaline basement-membrane, having a 

 glassy, transparent appearance, which is well marked 

 in the larger hair-follicles, but is not very distinct in 

 the follicles of minute hairs. It is continuous with the 

 basement-membrane of the surface of the corium. 

 External to this is a compact layer of fibres and 

 spindle-shaped cells arranged circularly around the fol- 

 licle. This layer extends from the bottom of the follicle as high as the entrance 

 of the ducts of the sebaceous glands. Externally is a thick layer of connective 

 tissue, arranged in longitudinal bundles, forming a more open texture and cor- 

 responding to the reticular part of the corium. In this are contained the blood- 

 vessels and nerves. 



The inner or epidermic layer is closely adherent to the root of the hair, so 

 that when the hair is plucked from its follicle this layer most commonly adheres 

 to it and forms what is called the root-sheath. It consists of two strata, named 

 respectively the outer and inner root-sheath ; the former of these corresponds with 

 the Malpighian layer of the epidermis, and resembles it in the rounded form and 

 soft character of its cells ; at the bottom of the hair-follicle these cells become con- 

 tinuous with those of the root of the hair. The inner root-sheath consists of a 

 delicate cuticle next the hair, composed of a thin layer of imbricated scales having 

 a downward direction, so that they fit accurately over the upwardly directed imbri- 

 cated scales of the hair itself; then of one or two layers of horny, flattened, 

 nucleated cells, known as Huxley's layer ; and finally of a single layer of horny 

 oblong cells without visible nuclei, called Henles layer. 



The hair-follicle contains the root of the hair, which terminates in a bulbous 

 extremity, and is excavated so as to exactly fit the papilla from which it grows. 

 The bulb is composed of polyhedral epithelial cells, which as they pass upward 

 into the root of the hair become elongated and spindle-shaped, except some in the 

 centre which remain polyhedral. Some of these latter cells contain pigment- 

 granules, which give rise to the color of the hair. It occasionally happens that 

 these pigment-granules completely fill the cells in the centre of the bulb, which 

 gives rise to the dark tract of pigment often found, of greater or less length, in 

 the axis of the hair. 



The shaft of the hair consists of a central pith or medulla, the fibrous part of 

 the hair, and the cortex externally. The medulla occupies the centre of the shaft 

 and ceases toward the point of the hair. It is usually wanting in the fine hairs 

 covering the surface of the body, and commonly in those of the head. It is more 



