STUDIES ON THE MAMMARY GLAND 429 
7. The walls of the milk-ducts are for the most part lined with 
a two-layered epithelium. The inner or glandular layer being 
composed of cuboidal to low columnar cells, while the outer (or 
so-called myo-epithelial layer) is composed of cells irregular in 
size, shape, and arrangement. At nine or ten weeks some of 
the terminal processes show indications of developing into alveoli. 
The walls of the intra-epidermal part of the primary duct are 
lined with stratified epithelium similar to that covering the 
surface of the nipple. 
8. Masses of subcutaneous fat develop soon after birth. Such 
masses Increase in size as age advances, and it is in this fat that 
many of the milk-ducts ramify. 
9. The stroma is divisible into its usual parts. The mantle 
layer forms a thin sheath immediately surrounding the milk- 
ducts. At the third week and thereafter elastic tissue fibers 
were visible in this layer surrounding the larger ducts. The 
true stroma is formed of a loose connective-tissue network in 
the early stages, but later shows a very marked infiltration of 
fat. Extending through the adipose tissue may be seen an 
occasional fair-sized connective-tissue lamina. 
10. In no stage was an infiltration of leucocytes observed in 
the stroma. 
11. A slight secretion appears in the lumina of the milk-ducts 
soon after birth. In no case has such secretion appeared in 
sufficient quantities to cause distention of the ducts. A trace 
of secretion may be seen in the milk-ducts through the ten weeks’ 
stage. Specific fat stains fail to reveal fat in the secretion of 
the milk-ducts or in the epithelial walls, notwithstanding the 
fact that much fat was seen in the true stroma outside the walls 
of the ducts. 
BIBLIOGRAPHY 
ANCEL, P., ET Bourn, P. 1909 Sur la fonction du corps jaune. Action du corps 
jaune vrai sur la glande mammaire (troisiéme note préliminaire). 
Compt. rend. Soc. Biol., T. 66, p. 605. 1911 Recherches sur les fone- 
tions du corps jaune gestatif. 11. Sur le détermimisme du développe- 
ment de la glande mammaire au cours de la gestation. Journ. dw phys. 
et de path. générale, no. 1, p. 31. 
