346 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



II. Outer root sheath; resembles Malpighian 

 layer of the epidermis. 

 III. Inner root sheath. 



1. Henle's layer, non-nucleated ele- 



ments. 



2. Huxley's layer, nucleated cells. 



3. Root sheath, structureless membrane. 

 The outer tunic is derived from the dermis and is 



of connective-tissue origin. Externally there is a 

 layer of connective-tissue fibers arranged longitudi- 

 nally, in which may be found a few connective- 

 tissue cells and a delicate plexus of nerve fibers. 

 The non-elastic connective-tissue fibers predominate, 

 but the elastic variety is also present. Internal to 

 the longitudinal fibers is a compact circular layer of 

 non-elastic connective-tissue fibers, and internal to 

 this is the glassy membrane, a very thin hyaline 

 sheath often difficult to find. The outer tunic in- 

 vests the lower half of- the root sheath. This tunic, 

 in the so-called tactile hairs of many mammals, has a 

 rich nerve innervation and a liberal blood supply. 

 In such hairs nerve fibers have been traced to the 

 glassy membrane, while others apparently penetrate 

 to tactile cells in the outer root sheath. 



The root sheaths encase the root of the hairs and 

 are derived from the epidermis, being therefore of 

 ectodermal origin. The outer root sheath is a direct 

 continuation of the Malpighian layer and diminishes 

 in thickness toward the bottom of the follicle. It is 

 composed of nucleated epithelial cells which possess 

 intercellular bridges and a fibrillar protoplasm. 

 This sheath always stains heavily with nuclear dyes, 



