NAILS. 329 



of the hyaline membrane, and by capillary loops which enter 

 the papilla. 



Little is known concerning the nerve-endings of the human 

 hair. In other mammals the nerves end below the sebaceous 

 glands. Medullated fibres lose their medullary sheaths, divide, 

 and penetrate to the hyaline membrane. Here some of the 

 branches encircle the hair, while others end freely on the 

 hyaline membrane as naked axis cylinders. These branch 

 regularly and run parallel to the long axis of the hair. 



The so-called tactile hairs of many mammals show an 

 especially rich inner vation. They are characterized by the 

 presence of well-developed blood spaces in the walls of the 

 hair follicle, and are therefore known also as sinus hairs. 

 In these hairs especially two kinds of nerve-endings are to 

 be noted : 



(a) The endings on the outer surface of the hyaline mem- 

 brane in the form of free arborizations ; and 



(b) The endings under the hyaline membrane in the outer 

 root sheath. These terminate by means of tactile menisci, 

 which are in contact with tactile cells. They resemble 

 strongly the tactile corpuscles of Merkel. 



(c) Nails. 



The nail is an epidermal structure. It lies on the corium, 

 which forms the so-called nail bed, and is surrounded by the 

 nail wall, which is formed from the skin (Figs. 250 and 252). 

 Between the nail wall and nail bed there is a groove, called 

 the nail groove.. The part of the nail visible to the naked 

 eye is called the nail body, while the posterior portion which 

 lies under the skin is the nail root. 



The connective-tissue nail bed forms ridges running for- 



c5 O 



ward along the nail and from the middle line out to the sides. 

 These become higher toward the free end of the nail, where 

 they are about 0.22 mm. Where the nail bed ends, in front, 

 we usually find skin papillae. 



In the nail bed lies the nail, which consists of two parts : a 

 soft layer, which represents the Malpighian layer of the skin ; 



