STUDIES ON THE MAMMARY GLAND 371 



During this week the abdominal and inguinal glands (fig. 11) 

 also undergo very rapid development. This is especially note- 

 worthy in view of the fact that the body weight of the rat from 

 which the gland at five weeks was drawn was practically the 

 same as that of the rat used at four weeks (fig. 10). The ducts 

 of the abdominal and first inguinal glands at five weeks (fig. 

 11) interlace very intricately. With the aid of the microscope 

 (especially the binocidar) one can be reasonably sure that many 

 of the ducts simply overlap, there being no anastomoses. How- 

 ever, there are areas in w^hich it is impossible to decide definitely 

 as to whether true anastomoses occur. This holds true in all 

 the later stages. Further investigations are necessary to deter- 

 mine this point concerning anastomosis. In this same week the 

 ducts of the second inguinal glands on each side have grown 

 cephalad to meet, and in some places even overlap, the ducts of 

 the first inguinal. Here the overlapping is not very compli- 

 cated and one can see distinctly that no anastomoses occur. 

 The ducts of the second inguinal gland taking a caudal direction 

 branch very profusely. 



Six weeks. At the end of the sixth week the glands do not 

 differ greatly from the five-weeks stage. Some of the glands, 

 the abdominal for example, show greater development. Others, 

 as the second inguinal, reveal no increase; in fact, in some speci- 

 mens they are less developed than those of the five-weeks stage. 

 The terminations of the ducts of the first and second inguinal 

 glands are separated from each other by considerable space. 



Seven iveeks. In the seventh week stage, the caudally directed 

 ducts of the first thoracic gland have made considerable advance 

 toward the cephalically directed ducts of the second thoracic 

 gland. However, they are still separated by a space of five to 

 eight millimeters in width. As in some of the previously de- 

 scribed stages the ducts of the second and third thoracic glands 

 overlap. The branching of the ducts of these glands is somewhat 

 more complicated at this stage. The abdominal and inguinal 

 glands (fig. 12) present very complicated systems of ducts; also 

 the overlapping between the ducts of the first and second ingui- 

 nal glands is very marked at this time. 



