74 The Development of the Lungs 
We are forced, however, to consider those animals in which these 
commonly suppressed elements are present. In these relationships we 
can see a reason why no Lateral 1 and Ventral 2 should form, but 
whether this stands absolutely in the relation of cause and effect, it is 
impossible from my material to say, as it is conceivably possible, although 
less probable for the condition te represent an adaptation on the part of 
the vessels to the use of unoccupied space. For either its absolute affir- 
mation or disproof, therefore, a series of animals, in which these ele- 
ments occur, must be examined from this standpoint during their 
developmental stages. This much may be said, however, in all of the 
lungs objectively pictured by Aeby, Huntington, and Narath where Lat- 
eral 1 is present on both sides, the one on the left-is usually lower than 
the corresponding branch on the right. In the instances where they 
are on the same level, both are so low that they do not interfere with 
the descent of the heart and great vessels. Similarly, a bronchus that is 
not situated on the left stem in the segment between L. 2 and L. 3 can- 
not be considered as the homologue of V. 2, the Bronchus infracardiacus. 
All other cases are substitution branches of the lateral bronchi or the 
stem. In the lungs which have been well pictured in the literature, 
where a real Ventral 2 occurs on the left stem, they are usually small 
and poorly developed and would not materially influence the migration 
of the Vena pulmonalis. It is also possible in these cases, as the veins 
are never drawn, that the latter have different relationships from those 
Influence of the Vessels upon the Architecture of the Bronchial Tree.— 
After following the development of the vascular system, we may con- 
sider now the possibility of the influence of the vessels upon the archi- 
tecture of the bronchial tree. Concerning the general asymmetry of 
the lungs, many of the older investigators have looked upon the heart 
or the great vessels as being responsible for this irregularity. Thus 
Bichat, 29, and Riidinger, 73, thought the left bronchus owed its greater 
length to the asymmetry of the heart, while Meyer, 61, looked upon the 
aortic arch as the factor which drew it out to greater length. In review- 
ing these statements, Aeby felt these authors passed over the most 
weighty relationship in overlooking the crossing of the bronchi by the 
arteries at a particular point on the stem to run down on its dorsal sur- 
face. This crossing enables the artery in the “hyparterial” to divide 
the side bronchi into a dorsal and ventral series, while the “ eparterial ” 
bronchi, situated above this separating influence of the artery, have their 
dorsal and ventral branches arising from a common stem. In quoting 
Kolliker’s observations on a 35-day human embryo, Aeby calls attention 
