Joseph Marshall Flint ak 
fourth lateral lies above and behind the bronchus, while the fourth ventral 
passes in a similar manner to those supplying the same series of bronchi 
in the upper part of the tree. The fourth dorsal runs backwards just 
lateral to the bronchus, maintaining, in general, this position as it rami- 
fies. In cases where there are median bronchi, as in this specimen, the 
artery passes medianwards around the dorsal surface of the stem and is 
placed dorsal to the bronchus during its ramification. The fifth lateral, 
ventral, and dorsal have corresponding positions to those of the higher 
orders, an] occupy the same relative positions. On the left side the 
pulmonary artery passes down without crossing the left bronchus at all 
to take its dorsolateral position to the stem. Just above the point of 
origin of left Lateral 2, the corresponding artery arises, and after pass- 
ing a short distance dorsosuperior to the bronchus, almost immediately 
divides, sending a branch to the apical bronchus which continues up- 
wards, placed laterally and dorsally to it. The remainder of the arteries 
on the left side have the same course as the corresponding branches on 
the right. In this description, I have followed strictly the typical 
specimens, although it is well to bear in mind that here, as in other 
parts of the vascular system, frequent variations are encountered. The 
veins still unite to empty into the left auricle through a common Vena 
pulmonalis. Branches from Lateral 1 and 2 form a common, large 
venous trunk on the right side, emptying directly into the Vena pulmo- 
nalis, while the vein from the left Lateral 2 joins the latter at a corre- 
sponding level on the opposite side. Below, the veins accompany the stem 
bronchi and their tributaries form a common trunk at the level of Lat- 
eral 3, which, crossing the ventral part of the stem bronchus between 
Lateral 2 and 38, empties into the pulmonary vein from below. The 
further growth of Ventral 2 on the right has gradually pushed the 
veins from the lower portion of the bronchial tree much more to the 
left, so that the large common trunk from the portion of the tree below 
Lateral 2 lies directly over the left axial bronchus at a point where the 
second ventral bronchus on that side would originate if the latter were 
present. It is this fact, as we have pointed out above, which has such 
great significance in explaining the suppression of that branch. From 
the ventrosuperior branch on the tracheal bronchus, the vein hes ventral 
and medial to it, receiving tributary vessels placed somewhat below the 
side branches of this bronchus. The vein from the dorsoinferior branch 
of Lateral 1 is placed ventralwards to that branch, and passes upwards 
to join the main trunk at a higher level. The main vein from Lateral 1, 
then passes down ventral to the artery and bronchus to form a common 
trunk with that from Lateral 2 as we have described above. The latter 
