THE SKIN. 



343 



Medulla. 



extensive nerve plexus, from which some terminal 

 fibers proceed to the hair follicles, and others to 

 special nerve papillae in the dermis. These and 

 other nerve terminations will be described as 

 peripheral nerve endings in another chapter. 



HAIRS. 



The hairs are distributed practically over the 

 whole surface of the body, with the exception of the 

 palms of the hand, the soles of the feet, and the red 

 border of the lips. They are distributed with con- 

 siderable regularity, as a 

 rule one hair for each fol- 

 licle, but there may be two 

 and sometimes three. The 

 part of the hair buried in 

 the skin is called the root, 

 and the part that projects 

 beyond the surface is the 

 shaft. The lower part of the 

 root is thickened to form 

 the hair bulb, into which is 

 pushed from below a vascu- 

 lar connective-tissue projection called the hair papil- 

 la. The root is inserted deep in the skin, usually 

 reaching the subdermal elements. It is placed 

 diagonally to the surface and becomes enclosed in a 

 specially modified wall made up of several layers de- 

 rived partly from the epidermis and partly from the 

 dermis. 



Most hairs are composed of three layers : an outer 

 cuticle, a middle cortical, and a central portion, the 



Cortical layer. 



Hair cuticle. 



Fig. 243. Portion of a hair. 



