325 



NORMAL HISTOLOGY. 



from cuticle. Greatly attenuated, it is prolonged over the hair-papilla, 

 which, as a special vascularized thickening of the connective tissue of the 

 follicle, carries nutrition to the bulb of the growing hair. 



The outer root-sheath is the continuation of the stratum germinativum 

 alone, the other layers of the epidermis thinning out and disappearing before 

 reaching the neck of the follicle. Its cells present the characteristics of those 

 of the germinating layer, with exceptionally well marked fibrillse. On ap- 

 proaching the level of the papilla, the outer root-sheath, which farther above 

 consists of numerous layers, rapidly diminishes in thickness until, on the 

 sides of the papilla, it is reduced to a single row of columnar cells. 



The inner root-sheath, which is best developed over the middle third 

 of the hair-root and fades away on reaching the upper third, includes three 



Theca folliculi 

 Middle layer 



Glassy membrane 

 Hair 



Cuticle of hair 

 ' and shealh 



i- Huxley's layer 

 and 



Henle's layer 



of inner root-sheath 



Outer root-sheath 



FIG. 370. Hair-follicle cut across about the middle, showing hair surrounded by the root-sheaths. X 285. 



layers. The outer, known as Henle 's foyer, consists of a single row of flat 

 polygonal cells, often partially separated by oval spaces. Their nuclei are 

 very indistinct or invisible within the cornified cytoplasm. The middle or 

 Huxley? s layer, also horny in nature, often comprises only one stratum of 

 nucleated cuboidal cells, but in the thicker hairs two or even three rows of 

 irregularly interlocked cells may be present. The third layer, known as the 

 sheath-cuticle, resembles the external coat of the hair, against which it lies, 

 in being extremely thin and composed of flat horny plates. The latter, 

 however, are always nucleated and so disposed that they are opposed to the 

 serrations of the thicker hair-cuticle. 



Traced towards the bottom of the follicle, the root-sheaths and the hair, 

 which above are sharply defined from one another, become more and more 

 alike until, in the immediate vicinity of the hair-papilla, they blend into a 

 still imperfectly differentiated mass of cells. The deepest elements of this 



