Fig. 4. Drawn from a section through the right second inguinal nipple of a 
female albino rat of six weeks. ep., epidermis adjacent to mammary gland area; 
ep.in., epithelial ingrowth; m.po., milk-pore; n., nipple; s., sulcus surrounding 
a part of base of nipple; se., secretion apparently solidified and dislodged from 
milk-pore. X 66-3. 
Fig. 5. Drawn from a section through the right first inguinal nipple of a fe- 
male albino rat of nine weeks. ep., epidermis; ep.in., epithelial ingrowth; h., 
hair follicle; x., nipple; p., process on epithelial ingrowth; p.d., primary duct; 
s., sulcus surrounding a part of base of nipple. At the bottom of this sulcus may 
be seen indications of degeneration. X 66-3. 
Fig. 6. Drawn from a longitudinal section through the primary duct of the 
right first inguinal gland of a female albino rat of nine weeks. c., collateral duct; 
l., lumen; p., primary duct proper. X 66}. 
407 
