10 Reticulated Basement Membranes in the Submaxillary Gland 
adjacent alveoli are not contiguous. The membranes stain an intense 
deep blue, like fine, delicate lines and are slightly thicker at the points 
where two adjacent membranes have fused than-at the boundaries of 
the small interalveolar spaces. The fibrillar nature of the membrane 
is shown in places where the alveolus and its membrane are cut tangen- 
tially. Now the interalveolar syncytium has almost entirely fused with 
the basement membranes, but here and there oval or lanceolate nuclei 
rest in close approximation to the developing membrana propria. 
These nuclei, however, are provided with very little protoplasm. From 
now on it is a very simple matter to follow the changes that occur in the 
transformation of the organ as it appears at 
birth to the conditions of adult life. In 
the adult gland there is between the alveoli 
an almost complete disappearance even of 
the small interalveolar spaces and the base- 
ment membranes of adjacent alveoli now lie 
fused together by the fibrils so that they 
form a single sharp distinct blue line which 
is separated here and there by the elongated 
nuclei of the connective tissue cells. At 
many nodal points the blood-vessels can be 
distinctly seen. In some places there is 
still a considerable amount of framework 
left especially in the regions about the lobu- 
lar ducts and those near the membrana 
FiG.8. Reticulated bas aoa 
aor beinee coated basement’ limitans of the lobule. .Hiyen “utidersiie 
alveoli of tk suk xi 7 = 7 
gland of a pis two dave aid. . Highest powers of the microscope these 
Stained by Mallory’ 
ariGr Zenker tata: Saori membranes appear as a homogeneous blue 
900 diameters. ae 
seca line except where the direction of the sec- 
tion yields a tangential view, and thus betrays to a certain extent their 
fibrillar nature. This, of course, is shown absolutely by the digestion 
methods. ‘To recapitulate, then, we see that the basement membranes 
are laid down almost simultaneously with the column of cells which 
springs from the buccal cavity and later forms by its dendronal branch- 
ing the gl. submaxillaris. This membrane is deposited partly in the 
syncytium in which it les and partly by increments derived from the 
exoplasmic fibrils of the embryonic connective tissue. As the ramifi- 
cation of the columns proceeds and the terminal buds of the growing 
gland come into closer approximation, the amount of syncytium be- 
tween them greatly diminishes and gradually takes on a more definite 
fibrillated structure until finally the two fuse and form a single mem- 
