306 



HISTOGENESIS 



The hair is differentiated from the basal epidermal cells surrounding the hair 

 papilla. These cells elongate and grow centrally toward the surface distinct 



Epitricbium 



Epidermal 

 anlage of 

 hair A 



Anlaqe of hair 

 hapilla 



*, Epidermaf. 

 anlage of hair B 



Stieath 



Hair bulb 

 flair papilla 



Fig. 293.— Section through the integument of the face of a 65 mm. embryo showing three stages in the 



early development of the hair. X 330. 



from the peripheral cells which form the outer sheath of the hair (Fig. 294). The 

 central core of cells gives rise to the inner hair sheath and to the shaft of the hair. 



At the sides of the outer hair 



Inner ha . 

 Sheath 



Outer hair 

 sheath 



~--^^ \Epidermts 



0/ir muscle fiber* 



91/ 



•Sebaceous glana. 



Mesenchymal /' 



Sheath 



Epithelial bed 



Hoot of hair 



■Hair bulb 

 fair papilla. 



Fig. 294. — Longitudinal section through a developing hair 

 from a five and one-half months' fetus (Stohr). 



sheath two swellings appear on 

 the lower side of the obliquely 



- directed hair anlage. The more 

 superficial of these is the anlage 

 of the sebaceous gland (Fig. 294). 

 The deeper swelling is the "epi- 

 thelial bed, " a region where the 

 cells by rapid division con- 

 tribute to the growth of the 

 hair follicle. 



Superficial to the bulb, the 



• cells of the hair shaft become 

 cornified and differentiated into 

 outer cuticle, middle cortex and 

 central medulla. The inner 

 hair sheath extends from the 



