360 



SPECIAL PHYSIOLOGY. 



being prolongations from the cutis; each follicle is lined by extensions 

 of the horny and soft layers of the cuticle, 1, 2, forming the part called 

 the root- sheath, the inner stratum of which adheres closely to the hair. 

 At the bottom of the follicle, is a more or less elevated portion of the 

 cutis, often forming a distinct papilla, 7, which is destitute of cuticle, 

 being covered, instead, by the attached extremity of the hair, which, 

 indeed, is formed on the papilla. The root of the hair is composed of 

 soft, pale, and somewhat compressed, nucleated cells; it is intimately 

 adherent to the root-sheath or cuticular lining of the follicle; when a 



Fig. 69. 



Fig. 69. Diagrams of the structure of the hair, hair follicle or sac, and sebaceous glands (Kolliker). a, 

 root of a hair, in its follicle. 1, outer, dry layer of cuticle. 2, Malpighitm or mucous layer, both dipping 

 into the 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 the hair grows. 1>, larger view of lower end of root of hair, and 

 bottom of hair sac. 6, the hair sac, showing the outer and inner root sheath, the latter adhering to the 

 hair. 7, the vascular papilla on which the hair grows. The hair itself shows its fibrous structure, its 

 dark medulla, and the transverse lines of its scaly covering, c. transverse section of a hair, showing its 

 outer covering, its fibrous part, and the central softer medulla or pith. (After Kolliker.) 



hair is plucked out, it comes away with this cuticular lining, which 

 clings closely round its root ; the vascular papilla at the bottom of the 

 follicle, however, remains, and a new hair is generated upon it. If 

 the papilla be destroyed by injury or disease, no new hair is formed. 

 The papillae resemble those on the surface of the true skin, being highly 

 vascular; all, except the papillae of the finest hairs of the body, prob- 

 ably receive nervous fibrils; for pain is produced when a hair is pulled 

 at, or plucked out. The papillae situated at the roots of the large 

 whiskers, or vibrissce of the cat, seal, and other animals, which are used 

 as feelers, are supplied with very large nerves. The hairs themselves 

 are destitute of nerves. 



It is on the papillae that the hairs are formed by the production and 

 metamorphosis of a succession of nucleated cells, as in the case of the 

 nails and epidermis. These cells undergo alterations for some distance 

 along the stem of the hair, which so becomes narrower than the root 

 or bulb. The softer central portion, whether deserving the name of 



