STUDIES ON THE MAMMARY GLAND 



363 



lei to the surface of the skin. In most cases observed the pri- 

 mary duct extends only a short distance until it divides into two 

 branches (secondary ducts) nearly equal in size. 



The extent of the primary duct varies considerably. For in- 

 stance, in the first thoracic and the last inguinal glands the pri- 



Fig. 5 Internal view of a wax model reconstructed from the left first inguinal 

 gland of a newborn albino rat. X 40. (For lettering, see fig. 3.) 



mary ducts present a rather extensive course before dividing, 

 while in the remaining glands they divide almost immediately 

 after making a sharp turn in the tela subcutanea. In figure 4 

 (last thoracic gland) the primary duct is seen to divide into three 

 branches. This is an exception to the general rule that the pri- 

 mary duct divides into two branches. 



