THE SKIN AND ITS ADNEXA. 22Q 



follicle sometimes extends into the subcutaneous 

 tissue, sometimes only into the corium, and its walls 

 are formed in the first place by a sheath of connec- 

 tive tissue continuous with the corium, in which 

 numerous blood-vessels ramify ; this sheath is lined 

 by a thin transparent membrane, called the vitreous 

 membrane. Within this follicular wall lies the root- 

 sheath, which consists of two layers : an outer 

 thicker layer, formed by the dipping down into the 

 follicle of the cells of the rete Malpighi, and hence 

 consisting of cylindrical, spheroidal, and somewhat 

 flattened cells ; and an inner layer made up in turn 

 of an external layer, called Henle 's sheath, in which 

 the cells resemble those of the horny layer of the 

 epidermis, and are closely packed together to form 

 a transparent mass ; and an internal layer, called 

 Huxley s sheath, whose cells, belonging more prop- 

 erly to the hair itself, are irregularly polygonal, some- 

 what flattened, and contain an elongated nucleus. 



Both at the opening of the follicle, and at its 

 base, the layers of the root-sheath become indis- 

 tinct, merging on the one hand into the cells of the 

 epidermis, and on the other into those of the hair- 

 bulb. At the bottom of the. follicle is a projection 

 from the connective tissue forming the wall of the 

 follicle, in the form of a papilla, which corresponds 

 to the papillae of the skin, and upon which the hair- 

 bulb rests, surrounding it at the top and sides. 

 The hair is produced by the growth of cells about 



