Joseph Marshall Flint 63 
about them, it is natural, with the venous outlet already established on 
the ventral side of the sacs, that the capillaries on the dorsal side should 
enlarge into arteries. Furthermore, after its origin and partial separa- 
tion from the cesophagus, the terminal part of the entire pulmonary 
apparatus extends somewhat ventralwards from the head gut making it 
additionally easier for the arteries to form on the dorsal than the ventral: 
surface of the anlage. ‘These factors are responsible for the course, 
which the arteries and veins take with reference to the bronchial tree, 
while the asymmetry of the stem bronchi appears to cause the chief dif- 
ference in the course of the arteries on the two sides. It is, further- 
more, possible that some of this irregularity is also due to the medial 
ScHEMA A. 
Schema to show the origin of the relations of the pulmonary vessels to the 
lungs. LA=Lung anlage. AP=Arteria pulmonalis. VP—=Vena pulmon- 
alis. L.1= Site of origin of Lateral 1 the “ eparterial bronchus.” L.2—=Site 
of origin of Lateral 2, the first bronchus in the “ hyparterial region.” L= 
Liver anlage. 
bending of the right artery in preparation for its transfer from the 
right to the left pulmonary arch according to the suggestion of Bremer, 
although in Bremer’s descriptions, with which my specimens agree, this 
actual transfer is made at a much later period, and I am accordingly 
inclined to minimize the possible influence of this factor. It is also 
worthy of note that we have no crossing of the bronchi by the arteries 
in the sense of Aeby. As they run down, they gradually turn dorsal- 
wards to take up a position behind the primitive sacs and are lost in the 
capillary plexus, which surrounds them. The pulmonary vein, scarcely 
