440 The Submaxillary Gland 
ing ducts, which we have termed the embryonic alveoli. The cells are 
polygonal in shape and have deeply staining nuclei, while the cytoplasm 
is granular. 
In a pig 84 centimeters long the.epithelial lining of the ducts of all 
orders from the ductus submaxillaris to the alveolus is in the form of a 
double row. The character of the epithelium is not changed from the 
simple form shown in the earliest embryos, where a similar condition 
also exists, but only in the larger ducts. 
In a pig 124 centimeters long, the rami principales, interlobulares and 
sublobulares are already formed. At this time the epithelium of the 
inner layer of the ducts ‘of the lower orders shows a tendency to become 
columnar, the nuclei ovoid, with their long axes parallel to the long 
axis of the cell. The epithelium of the outer layer is more irregular 
and conical in shape, while the nuclei are rounded and vesicular. The 
portion corresponding to the intercalary ducts in the adult now joins 
the alveolus directly to the sublobular duct. This indicates accordingly 
that ducts of the lobular order have not yet been formed, but in these 
intercalated portions, the cells appear quite like the parietal cells of the 
alveoli, and are arranged in two definite strata. 
At 19 centimeters there is no change in the ducts of the higher order, 
but, with the definite appearance of the secondary lobules, we note the 
formation of the lobular and intralobular ducts for the first time. The 
epithelium of both orders is in two layers, an inner cubical and an outer 
more irregular layer. The ducts connecting them with the acini show 
a considerable flattening with a tendency for the inner stratum to take 
the stain more intensely than those of the outer layer. 
At 22 centimeters the ducts of the higher order show an increase in 
the columnar arrangement of the inner layer of cells; the central por- 
tions now stain a deep blue with a clearer peripheral portion on the 
side of the nucleus near the basement membrane. ‘The ducts of the sub- 
lobular, lobular and intralobular order remain unchanged. Definite 
imtercalary ducts have now been formed and appear to have but a single 
layer of epithelium with the long axis of the nuclei parallel to the axis 
of the duct. 
In a pig 264 centimeters long the main ducts have now a distinct 
columnar epithelium adjacent to the lumen. ‘This has-a bluish staining 
pole and a clearer peripheral pole. As the ramification proceeds, par- 
ticularly in ducts of the sublobular order, there is a tendency for the 
epithelium to become more columnar. There is no striation in the cyto- 
plasm of the cells of the intralobular ducts. These now appear in many 
