STUDIES ON THE MAMMARY GLAND 409 
ally becomes thinner until it forms only an extremely thin layer 
around the terminal ducts. Previous to the third week, no elastic 
tissue fibers were observed in the mantle layer. At the end of the 
third week, however, Weigert’s resorcin-fuchsin stain reveals a 
few elastic tissue fibers sprinkled among the other fibers of the 
mantle layer of the primary and secondary ducts. During the 
fifth, sixth, and seventh weeks more elastic fibers are present in 
the sheath of the primary and secondary ducts, and they are 
found in the sheath nearer the free end of a system of ducts than 
at three weeks. ‘The true stroma is formed of loose connective- 
tissue in which various kinds of leucocytes are found. In no 
instance has an abnormal number of leucocytes been observed. 
The stroma also presents a great deal of adipose tissue. The 
connective tissue which occupies the nipple and epithelial hood 
is much more compact than in other parts of the gland. 
About the third week the free ends of the milk-ducts of the 
abdominal and inguinal glands are observed to extend some dis- 
tance into the inguinal fat pad where they send off numerous 
ramifications. As age advances the fat pad becomes more 
voluminous. It is not only thicker and longer, but wider than 
in the preceding stages. Hence its medial margin extends to the 
level of the abdominal and inguinal nipples. A great deal of 
adipose tissue has developed also in the stroma of the thoracic 
glands, so that the ramifications of many of the ducts are sur- 
rounded by fat cells. 
Eight, nine, and ten weeks 
It may be recalled that between the eighth and tenth week it 
was found in an earlier work (Myers, ’16) that the ducts of the 
mammary gland of the female grow and proliferate very rapidly. 
Cleared preparations show that a tremendous number of new 
ducts bud out from the already existing ducts. These ducts bud 
off not only at the ends of the terminal ducts, but also as collateral 
ducts from the sides of all other ducts represented, including that 
part of the primary duct which lies parallel with the surface of the 
skin. In some of the ten weeks’ stages the proliferation of ducts 
is not as marked as in those of nine weeks. 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 25, NO. 4 
