STUDIES ON THE MAMMARY GLAND 203 



primary duct anlage is roughly L-shaped with its attached end 

 perpendicular and its free end parallel to the surface (figs. 2 

 and 8). The anlage in elongating has pushed ahead of it the 

 above mentioned layers of condensed mesenchyma representing 

 the corium and tela subcutanea. These layers now completely 

 surround the free part of the anlage. In the first thoracic gland 

 the free end of the anlage is directed cephalad. In the second 

 inguinal gland, the free end points caudad. Likewise the free 

 end of each of the remaining ducts is directed toward the position 

 which the future duct and its branches will occupy. 



The anlages of the ducts are longer than in the seventeen day 

 and two hour stage. In one of the first thoracic glands of one 

 fetus and in one of the abdominal glands of another fetus the 

 primary duct presents two secondary ducts (fig. 17, s.d.). All 

 other glands observed at this stage possess a single undivided 

 primary duct. 



When seen in cross section at this stage, the primary duct of 

 most of the glands possesses a basal layer of cuboidal cells with 

 large oval nuclei. The basal ends of the cells rest on a some- 

 what indistinct basement membrane while the opposite ends are 

 directed toward the center of the duct. The center of the duct 

 is filled with cells of irregular shape. Somewhat nearer the free 

 than the attached end of some of the ducts the cells occupying 

 the center of the duct show a tendency toward separation from 

 each other. In other ducts some of the central cells have en- 

 tirely separated, thus producing small cavities or lacunae, the 

 first appearance of a very indefinite lumen (fig. 4). Such a 

 condition obtains in many of the thoracic and abdottiiinal glands 

 examined, but is very rare in the inguinal glands of this stage. 

 It is interesting to note that in the thoracic and abdominal 

 glands which have already developed secondary ducts, only one 

 of these ducts shows a slight indication of a lumen. The mes- 

 enchymal cells of the corium and tela subcutanea are somewhat 

 condensed around the ducts. Those nearest the ducts are 

 much elongated and are concentrically arranged. 



In one abdominal gland about h^lf way between the outlet 

 and mouth of the funnel the cells of the stratum germinativum 

 have slightly elongated thus forming a low ridge which projects 



