Proceedings of the Association of American Anatomists Vv 
teries corresponds to the branching of the bronchi, along which numer- 
ous small rami continually spread themselves out to form an irregular 
plexus, in general arranged at right angles to the muscular layer. In a 
collapsed lung the bronchial arteries have a tortuous course, but when 
the lung is inflated and the bronchi correspondingly lengthened their 
course is quite straight. The main trunks can be followed as far as the 
kronchioli respiratorii where they terminate in a capillary network which 
extends to the distal end of the ductuli alveolares. ; 
From the arterial plexus in the fibrous layer small twigs are given off 
which penetrate through the muscular layer and having reached a posi- 
tion beneath the epithelium lining of the bronchi they turn and run for a 
short distance parallel with the muscular layer, giving off capillaries 
which run parallel to the long axis of the bronchus. These capillaries 
unite to form a network of venous radicles situated at first side by side 
with the arterial radicles, then passing obliquely through the muscular 
layer they form a second plexus, with a coarse mesh, along the boundary 
line between the fibrous and muscular layers. 
From this second venous plexus small veins arise which form one of 
the sources of origin of the pulmonary vein. These small veins, which 
may be designated as broncho-pulmonary (Le Fort), arise at various in- 
tervals along the larger bronchi; along the smaller bronchi and the 
bronchioli respiratorii they usually arise, one on either side, at the 
place where the bronchi divide; from the ductuli alveolares they arise one 
on either side of their distal end and carry off from the bronchial tree 
the last trace of blood which is found in the terminal capillary network 
into which the main trunks of the bronchial arteries break up. 
By a careful study of the vascular network in the bronchial muscosa 
one can recognize small areas composed of an arterial radicle, its capil- 
laries and a loop of the venous plexus. I have found this area in the 
bronchi of man, the dog and the cat. It may be called the unit of dis- 
tribution. 
The veins arising from the first two or three divisions of the bronchi 
do not join the pulmonary vein, but form true bronchial veins which 
empty into the azygos or into the vena cava. This has already been noted 
by several authors. 
No anastomoses were found between the bronchial and pulmonary ar- 
teries. In many sections quite large branches could be seen passing from 
the bronchial arteries to the walls of the pulmonary artery where they 
became the vasa vasorum, but in no instance was the differential injection 
mass found in the lumen of the pulmonary artery. 
