402 J. A. MYERS 
cephalad, we find a very gradual elevation until the highest part 
of the nipple is reached. If we start a short distance cephalic 
to the nipple, we enter a shallow groove or sulcus before reaching 
the base of the nipple. From the bottom of this groove we find 
a steep approach to the summit of the nipple elevation. The 
groove appears cephalic to and passes slightly to the medial and 
lateral sides of the nipple. In the case of the second and third 
thoracic glands, the abdominal gland and the first inguinal gland, 
the groove is on the medial side and extends slightly to the 
cephalic and caudal parts of the base of the nipple (fig. 5). It 
is absent on the lateral side of the nipple. In the second inguinal 
nipple the relations of the groove to the nipple are just opposite 
to those in the first thoracic. Near the highest part of the nipple 
the lumen of the intra-epidermal portion of the primary duct 
appears somewhat deeper than when it was observed in an 
earlier stage. 
The projection of the epithelial hood extends more deeply 
into the corium than in the earlier stages (fig. 3). The pro- 
cesses which appeared on the epithelial projection in rats of one 
day are now longer and have the appearance of rather sharp 
‘spines. A few of them possess secondary processes. 
The lumen of the primary duct now extends nearer to the sur- 
face, yet it is not in continuity with the lumen of the intra- 
epidermal part of the duct. No degenerating cells have been 
observed in the formation of the lumen of the primary duct 
proper. This lumen apparently is formed by a process of re- 
arrangement of cells as was shown to be the case (Myers, 717 a) 
in the other milk-ducts of the fetus. From the secondary ducts 
through the terminal ducts the amount of secretion present in 
lumina has increased somewhat since the end of the first day. 
While it is present in considerable quantities, yet the ducts are by 
no means engorged. In sections stained with Weigert’s iron- 
haematoxylin the secretion fails to take the stain, while in those 
stained with Dominici’s mixture it takes a light pink color. In 
fresh frozen sections very rarely a fat droplet was observed in the 
walls of the milk-ducts. The infrequency of such droplets, their 
relation to the cells, and their absence in sections fixed, sectioned 
