94 GENERAL ANATOMY. 



connective tissue, arranged in longitudinal bundles, in which 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; then of one or two layers of horny, flattened, 

 nucleated cells, known as Huxley s layer ; and finally of a single layer of non- 

 nucleated, horny, flattened cells, called Henle's 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 

 opaque and deeper colored when viewed by transmitted light than the fibrous part ; 

 but when viewed by reflected light it is white. It is composed of rows of poly- 

 hedral cells, which contain air-bubbles. The fibrous portion of the hair consti- 

 tutes the chief part of the shaft ; its cells are elongated and unite to form flattened 

 fusiform fibres. Between the fibres are found minute spaces which contain either 

 pigment-granules in dark hair or minute air-bubbles in white hair. In addition 

 to this there is also a diffused pigment contained in the fibres. The cells which 

 form the cortex of the hair consist of a single layer which surrounds those of 

 the fibrous part ; they are converted into thin, flat scales, having an imbricated 

 arrangement. 



Connected with the hair-follicles are minute bundles of involuntary muscular 

 fibres, termed arrectores pili. They arise from the superficial layer of the corium, 

 and are inserted into the outer surface of the hair-follicle, below the entrance of 

 the duct of the sebaceous gland. They are placed on the side toward which the 

 hair slopes, and by their action elevate the hair (Fig. 68). 



The sebaceous glands are small, sacculated, glandular organs, lodged in the 

 substance of the corium. They are found in most parts of the skin, but are most 

 abundant in the scalp and face : they are also very numerous around the apertures 

 of the anus, nose, mouth, and external ear ; but are wanting in the palms of the 

 hands and soles of the feet. Each gland consists of a single duct, more or less 

 capacious, which terminates in a cluster of small secreting pouches or saccules. 

 The sacculi connected with each duct vary, as a rule, in numbers from two to five, 

 but, in some instances, may be as many as twenty. They are composed of a 

 transparent, colorless membrane, enclosing a number of cells. Of these the outer 

 layer or marginal cells are small, polyhedral, epithelial cells, continuous with the 

 lining cells of the duct. The remainder of the sac is filled with larger cells, con- 

 taining fat, except in the centre, where the cells have become broken up, leaving 

 a cavity containing the ddbris of cells and a mass of fatty matter, which consti- 

 tutes the sebaceous secretion. The orifices of the ducts open most frequently into 

 the hair-follicles, but occasionally upon the general surface. On the nose and face 

 the glands are of large size, distinctly tabulated, and often become much enlarged 



