24 COMPARATIVE ANATOMY 



medulla, cortex, and cuticle (Fig. 16 A), all of which are formed 

 from cells. The follicular tissue, which is richly provided with 

 blood-vessels, extends into the bulb-like base or root of the hair- 



HP 



FIG. 15. DIAGRAMS OF FOUR STAGES (A-D) IN THE DEVELOPMENT OF HAIRS, 



(After F. Maurer.) 



Sc, stratum corneum ; SM, stratum Malpighii, which gives rise to an epithelial 

 knob at Ep ; this grows inwards into the dermis (C) ; F, rudiment of the hair- 

 follicle ; HP, hair-papilla ; HK, hair-bulb ; Dr, rudiment of the sebaceous 

 gland. In D, /, indicates the stratum lucidum with eleidm-granules in the 

 cells. 



shaft, and gives rise to the hair-papilla. From this region a new 

 hair-shaft may develop when the hair is shed, periodically or n on- 

 period ically as the case may be, often by the formation of a new 

 papilla. The colour of the hair is due to three causes : Firstly, 



