348 HANDBOOK OF PHYSIOLOGY. 



gradually thicker as it moves to the front, until, projecting be} 7 ond the 

 surface of the matrix, it can receive no fresh addition from beneath, and 

 is simply moved forwards by the growth at its root, to be at last worn 

 away or cut off. 



FUNCTIONS OF THE SKIN. 



(1.) By means of its toughness, flexibility, and elasticity, the skin 

 is eminently qualified to serve as the general integument of the 

 body, for defending the internal parts from external violence, and readily 

 yielding and adapting itself to their various movements and changes of 

 position. 



(2.) The skin is the chief organ of the sense of touch. Its whole 

 surface is extremely sensitive; but its tactile properties are due more es- 



Fio. 240. Transverse section of a hair and hair-follicle made below the opening of the sebace- 

 ous gland, a, medulla or pith of the hair; &, fibrous layer or cortex; c, cuticle; d, Huxley's layer; 

 e, Henle's layer of internal root-sheath; / and#, layers of external root sheath, outside of g is a 

 light layer, or " glassy membrane," which is equivalent to the basement membrane: 6, fibrous coat 

 of hair sac; i, vessels. (Cadiat.) 



pecially to the abundant papillae with which it is studded. (See Chapter 

 on Special Senses.) 



Although destined especially for the sense of touch, the papillae are 

 not so placed as to come into direct contact with external objects; but 

 like the rest of the surface of the skin, are covered by one or more layers 

 of epithelium, forming the cuticle or epidermis. The papillae adhere 

 very intimately to the cuticle, which is thickest in the spaces between 

 them, but tolerably level on its outer surface: hence, when stripped off 

 from the cutis, as after maceration, its internal surface presents a series 

 of pits and elevations corresponding to the papillae and their interspaces 



