STUDIES ON THE MAMMARY GLAND 397 
ED. S. 1. 
Fig.1. Drawn from a section through the left first inguinal nipple of a female 
albino rat at birth. ep., epidermis adjacent to mammary gland area; ep. in., 
epithelial ingrowth or hood; /., lumen; n., nipple; p.d., primary duct. X 100. 
Fig. 2. Drawn from a section through the left second thoracic nipple of a 
female albino rat of one.day. ep., epidermis adjacent to mammary gland; ep. in., 
epithelial ingrowth; h., hair follicle; n., nipple; p., developing processes on epi- 
thelial hood; p.d., primary duct. X 100. 
Fig. 3. Drawn from a section through the right third thoracic nipple of a 
female albino rat of five days. ep., epidermis adjacent to mammary gland; ep. 
in., epithelial ingrowth; h., hair follicle; n., nipple; p., developing processes on 
epithelial hood; s., sulcus partially surrounding nipple. X 100. 
