SEBACEOUS GLANDS. 



83 



with the outer coat of the hair-follicle, and the thin, dry, and scaly character 

 of those which lie near the surface of the hair, to which they are closely adhe- 

 rent. When the hair is plucked from its follicle, this cuticular lining most 

 commonly adheres to it, and forms what is called 

 the root-sheath. 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 follicle, is highly 

 vascular, and probably supplied with nervous 

 fibrils. This is the part through which material 

 is supplied for the production and constant 

 growth of the hair. The root of the hair rests 

 upon this conical-shaped eminence, and is con- 

 tinuous with the cuticular lining of the follicle 

 at this part. It consists of nucleated cells, simi- 

 lar in every respect to those which in other 

 situations form the epidermis. These cells 

 gradually enlarge as they are pushed upwards 

 into the soft bulb, and some of them contain 

 pigment granules, which either exist in separate 

 cells, or are separate, or aggregated round the 

 nucleus; it is these 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 track of pigment often found, of 

 greater or less length, in the axis of the hair. 



The shaft of the hair consists of a central part 

 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 com- 

 monly in those of the head. It is more opaque 

 and deeper colored than the fibrous part, and 

 consists of cells containing pigment or fat-gran- 

 ules. The fibrous portion of the hair constitutes 

 the chief part of the stem ; its cells are elongated, and unite to form flattened 

 fusiform fibres. These also contain pigment granules, which assume a linear 

 arrangement. The cells which form the cortex of the hair consist of a single 

 layer which surrounds those of the fibrous layer; they are converted into thin 

 flat scales, having an imbricated arrangement. 



The Sebaceous Glands are small, sacculated, glandular organs, lodged in the 

 substance of the corium, or subdermoid tissue. 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 con- 

 sists of a single duct, more or less capacious, which terminates in a lobulated 

 pouch-like extremity. The basement membrane forming the wall of the sac, 

 as well as the duct, is lined by epithelium, which is filled with particles of se- 

 baceous matter; and this becoming detached into the cavity of the sac, as its 

 growth is renewed, constitutes the secretion. The sacculi connected with each 

 duct varv in number from two to five, or even twenty. 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 

 lobulated, and often become much enlarged from the accumulation of pent-up 



Diagram of structure of hnir, hair 

 follicle, and sebaceous glands (Kb'lliker). 

 . Root of hair, in its follicle. 1. Outer 

 dry layer of cuticle. 2. Malpighian or 

 mucous layer, both dipping into hair sac. 

 3. Cutis, or true skin. 4. Sebaceous 

 glands, opening into hair sac. 5. Root 

 of hair. 6. Walls of hair sac. 7. Papilla, 

 on which hair grows, b. Larger view 

 of lower end of root of hair, and bottom 

 of hair sac. 6. Hair sac, showing outer 

 and inner root-sheath, latter adhering 

 to hair. 7. Vascular papilla on which 

 hair grows. The hair itself shows its 

 fibrous structure, its dark medulla, and 

 transverse lines of its scaly covering. 

 c. Transverse section of a hair, showing 

 its outer covering, its fibrous part, and 

 central softer medulla or pith.] 



