424 The Submaxillary Gland 
of adjacent alveolar groups. ‘The meshes are small and regular, and 
occupy three dimensions. ‘This plexus has anastomoses extending 
throughout the lobule, but terminates on all sides at the membrana 
limitans. Each lobule has, therefore, with certain exceptions that will 
be considered later, an independent circulation. 
Beginning in small radicals around the base of the alveoli, venules 
are formed through the coalescence of capillaries. These rapidly con- 
verge to a point near the terminal arterioles about the intercalary duct 
to form venae terminales. The veins are short and there is but a single 
one accompanying each terminal arteriole. At the point of junction of 
several intercalary ducts, the accompanying terminal veins through 
their confluence form the intralobular veins which collect the blood 
from different portions of the lobule and terminate in the lobular vein. 
This vessel makes its exit from the lobule at the hilus, side by side with 
the lobular artery. There is no reduplication of the veins of the intra- 
lobular system. As soon as the veins leave the lobules, however, and 
enter the sublobular interspaces, the venous system is doubled, yielding 
venae comites to each successive division of the A. submaxillaris. The 
sublobular veins parallel the course of the artery, giving off numerous 
anastomotic branches which run over and under the artery forming 
oblong meshes. It is not uncommon, however, to have the veins sepa- 
rate and pass around the duct and then join on the opposite side, or else 
have anastomotic branches pass from the venae comites, embrace the 
duct, and finally joi the main veins lower down. The vene comites 
with their blood current flowing in the reverse direction follow in a 
convergent manner the previous divergence of the arteries. Thus the 
sublobular veins unite to form those of the interlobular system, while 
these, in turn, join to make the venae principales. The principal veins 
part with the ducts at the same point where the artery joins them and 
leave the gland along with the A. submaxillaris as the Venae submaxil- 
lares. These usually empty into the vena facialis communis. In the 
general glandular circulation we find two vascular units, one, a complete 
terminal system, forming, in Ludwig’s sense, the true unit of circula- 
tion, that is to say, blood-vessels supplying a group of structures which 
have definite relations throughout the organ with the general frame- 
work. These form, in this way, the ultimate indivisible complete wnit 
of structure of which the organ is built up. Such a unit in the sub- 
maxillary gland would be represented by the lobule and the whole organ 
is simply formed of a series of these units. Another vascular unit could 
be formed of the terminal arteries. These break up in the alveolar 
capillary plexus which reunite into small venule radicals and empty 
