STITDIES ON THE MAMMARY GLAND 199 



distance as described by Jackson ('12) in determining the sex 

 of the newborn. In the earher fetal stages the sex was deter- 

 mined by studying the developing reproductive organs. 



The' wax reconstructions w^ere made according to Born's 

 method. 



OBSERVATIONS 



Henneberg states that in fifteen day and fourteen hour em- 

 bryos the six pairs of mammary glands occupy their definitive 

 positions. Since Henneberg made only a macroscopic study of 

 the glands at this stage, a further account is here given of the 

 condition found in embryos of nearly the same age. 



Fifteen days. On the surface of the skin at this stage (fif- 

 teen days and nine hours) is a small eminence (fig. 7) over each 

 developing gland. Such eminences are very prominent in fresh 

 preparations. A cross section through a gland (fig. 1) shows 

 that the epidermis in the neighborhood of the gland is composed 

 of only two layers, a superficial layer (periderm) of flattened 

 cells with their long axes parallel to the surface, and a deeper 

 layer (stratum germinativum or Malpighian layer) of round or 

 cubical cells. The nuclei of the latter layers are located toward 

 the free end of the cells. The basal ends of the cells have a 

 quite clear appearance and rest on a definite basement membrane 



(% 1). 



The basement membrane dips down into the underlying mesen- 

 chyma to surround the spheroidal mass of epithelial cells form- 

 ing the gland anlage. Likewise the stratum germinativum of the 

 epidermis passes deep around the same circular mass of cells and 

 forms the basal layer of the mass. The cells of the spheroidal 

 mass are differentiated and arranged so that they possess a 

 characteristic appearance. The cells of the basal layer appear 

 much more elongated than those in the stratum germinativum 

 of the adjacent epidermis. The cells occupying the center are 

 irregular in shape and closely packed. 



Superficially the gland anlage projects somewhat producing 

 the eminence \dsible from the surface. Around its deep surface 

 the mesenchyma is condensed. The mesenchymal cells lying 



