394 The Vascular Supply of the Pleura Pulmonalis 
The under surface of the lymphatics is apparently supplied by the 
capillary network of the air sacs (sacculi alveolares), over which they 
run, since encircling loops are rarely present in my preparations. 
When the lymphatics are collapsed, the relation of the blood-vessels 
to the lymph vessels is not so apparent; it is only when the lymph 
vessels are distended that the relationship is best seen. On the other 
hand, having become familiar with this relationship, the situation of the 
lymphatics can be made out from the course of the blood-vessels, when 
they are well injected. 
The capillary network of blood-vessels, which belongs to the remaining 
portion of the pleura, though continuous with that over the lymphatics, 
differs in the size and shape of its mesh and is readily distinguished from 
that over the lymphatics (Fig. 3). The entire network of pleural capil- 
laries discharges its blood into the radicles of the pulmonary vein. 
That which I have figured in a previous contribution (9c) as the 
capillary network of the pleura belongs to the peripheral walls of the 
sacculi alveolares and not to the pleura proper. The mesh of the system 
of capillaries belonging to the sacculi alveolares, just beneath the pleura, 
is much coarser than that of the sacculi alveolares in the depth of the 
lung; that belonging to the pleura itself is still coarser. 
Sheep.—tIn the sheep, the pleura receives its vascular supply in a 
manner quite different from that in the dog. Though thus far I have 
failed to demonstrate the bronchial artery as being distributed to the 
pleura of the dog, the first injection made showed a rich distribution of 
the bronchial artery to the pleura of the sheep. 
From the hilus of each lung, and from a main trunk which runs along 
the pulmonary attachment of the ligamentum pulmonale, branches of the 
bronchial artery can be seen passing to all the lobes of the lung (Fig. 4). 
In general, the main branches on the facies mediastinalis and facies 
diaphragmatica may be said to run parallel to each other. These main 
branches are connected by numerous anastomoses and there is thus formed 
a coarse plexus of vessels the mesh of which is occupied by a network of 
still finer vessels. 
Figure 4 shows several branches of the branchial artery entering the 
incisura interlobaris. These branches are distributed to what may be 
called the facies interlobaris of the superior and inferior lobes of the lung. 
The facies costalis (Fig. 5) receives its vascular supply in quite a 
different manner. Branches of the bronchial artery extend over the margo 
inferior and the margo anterior to the facies costalis and there break up 
