208 



THE SKItf 



cent portion of the horny layer in the immediate neighborhood of 

 the duct is invaginated into the stratum mucosum, which is thus 

 considerably thinned by the passage of the duct. 



The sweat glands are abundantly supplied with capillary blood 

 vessels and small nerves, which form plexuses about the walls of 

 the coiled portion of the gland, and from which terminal fibrils 

 penetrate the basement membrane and end in contact with the 

 secreting cells. 



Development. The sudoriparous glands first appear in the 

 embryo during the fifth month as solid columnar ingrowths from 

 the stratum germinativum of the epidermis. These processes 

 grow inward through the primitive corium to its junction with 

 the looser subcutaneous tissue. Here the cell columns become 

 thickened and convoluted, and at about the same period their 

 lumen appears. The glandular lumen is not at first connected 

 with the free surface, but as the cells of the germinal layers of the 

 epidermis gradually replace those which are more superficial the 

 epidermal portion of the duct is formed. At about the seventh 

 month the lumen of the duct opens upon the epidermal surface. 



The membrana propria of the fundus and dermal portion of 

 the duct are derived from the surrounding connective tissue ele- 

 ments of the mesenchyma. 



c f e g 



FIG. 183. THE DORSAL HALF OF THE TIP OF AN INFANT'S FINGEK, SHOWING THE 'NAIL 



IN SECTION. 



a, nail root; '>, free extremity; c, eponychium; d, hyponychium; e, nail; /, stratum 

 mucosum of the nail ; g, nail bed ; A, bone. Hematein and eosin. Photo, x 23. 



THE NAILS. The nails are produced by a peculiar modifica- 

 tion of the epidermis by which the stratum lucidum becomes 

 greatly thickened while the horny layer is at the same time want- 

 ing. The nail is divisible into the nail ~body and nail root ; the 



