MAMMARY GLANDS 



297 



tissue which surrounds the hair folhcle in the neighborhood of the epithehal bed 

 gives rise to the smooth fibers of the arredor pili muscle. Pigment granules de- 

 velop in the basal cells of the hair and give it its characteristic color. 



Epidermis 



— Sebaceous gland 



rector pili muscle fibers 



Outer lidir sliciilh 

 Mesenchymal 



Epithrlial bed 



Root of hair 



lb 

 pi II a 



Fig. 301. — Longitudinal section through a developing hair from a five and one-half months' human 



fetus (after Stohr). X 220 



The first generation of hairs are short-lived, all except those covering the face 

 being cast off soon after birth. The coarser replacing hairs develop, at least in 

 part, from new foUicles. Thereafter hair is shed periodically throughout life. 



SWEAT GLANDS 



The sweat or sudoriparous glands begin to develop in the fourth month from 

 the epidermis of the finger tips, the palms of the hands, and the soles of the feet. 

 They are formed as solid downgrowths from the epidermis, but differ from hair 

 anlages in having no mesenchymal papillae at their bases. During the sixth 

 month the tubular anlages of the gland begin to coil and in the seventh month 

 their lumina appear. The inner layer of cells forms the gland cells, while the outer 

 cells become transformed into smooth muscle fibers which here arise from the 

 ectoderm. In the axillary region sweat glands occur which are large and branched. 



MAMMARY GLA^fDS 



The tubular mammary glands peculiar to mammais are regarded as modified 

 sweat glands. In embryos of 9 mm. (Figs. 94 and 118) an ectodermal thickening 



