THE HAIR 



213 



and a central Jiair. Continued multiplication of the cells in the 

 germinal layer of the bulb pushes the advancing tip of the hair 

 nearer and nearer the surface until it forces its way into the 



FIG. 186. FROM A SECTION OF THE SKIN OF AN INFANT'S ARM, SHOWING SMALL 



IMMATURE HAIR FOLLICLES IN TRANSECTION. 



a-a, epidermis ; i-6, derma ; c-c, subcutaneous connective tissue ; d-d, muscle. Hematein 

 and eosin. Photo, x 95. 



epidermal hair canal. Finally the thin cuticular covering is 

 ruptured and the eruption of the hair shaft occurs. 



Further differentiation of the cells of the epidermal root sheath 

 and the formation of a mesenchymal or dermal sheath of connec- 

 tive tissue completes the development of the hair follicle. This 

 process is frequently repeated and results in the formation of new 

 hairs not only during fetal life, but also, in constantly decreasing 

 numbers, throughout childhood and adult life. 



