398 J. A. MYERS 
Traced toward the nipple from the free end of the epithelial 
projection the stratum germinativum extends toward the sur- 
face of the skin thus lining the inner surface of the epithelial 
hood. Traced away from the nipple from the free end of the 
epithelial projection it forms the outer surface of the projection 
and becomes continuous as the stratum germinativum of the 
surrounding integument. Mitotic figures are numerous in the 
stratum germinativum covering the epithelial projections. 
The contents of the hood are densely arranged connective- 
tissue cells, small blood-vessels, small nerves, white blood cor- 
puscles, and the developing primary milk-duct. The connective- 
tissue cells are densely placed as in other parts of the corium. 
Near the walls of the epithelial hood these cells are arranged 
somewhat parallel to the stratum germinativum. In other parts” 
of the hood they are arranged in a more irregular manner except 
around the developing primary duct, where they are concentri- 
cally placed, thus forming the sheath of the duct. 
In microscopic sections near the highest part of the developing 
nipple a very shallow pit is being formed by the process of des- 
quamation. This pit represents the future opening of the pri- 
mary milk-duct—the milk-pore. As this pit deepens in the later 
stages it becomes a part of the lumen of the primary milk-duct. 
This part of the lumen becomes greater in extent than the 
thickness of the epidermis covering the nipple, for the sake of 
convenience in description, however, it shall hereafter in this 
paper be known as the intra-epidermal part of the primary duct. 
From this very shallow pit a solid cord of cells extends through 
the thickened epidermis. This is the anlage of the intra-epider- 
mal portion of the primary milk-duct. At birth there is no trace 
of a lumen in this portion of the duct. That part of the duct 
within the epithelial hood takes a course perpendicular to the 
surface of the integument. Near the surface the duct is repre- 
sented by a solid cord of cells, but as it is traced deeper an oc- 
casional lacuna representing the first trace of a lumen is encoun- 
tered. In some glands several lacunae have flown together, thus 
representing a larger lumen with an irregular outline (fig. 1). 
The cells in the walls of this part of the duct present no definite 
