114 The Development of the Lungs 
His, Willach, Robinson, d’Hardiviller, and Miller, either actively or 
passively, support the views of Aeby, while Ewart, Zumstein, Narath, 
Minot, Huntington, Justesen, and Merkel have abandoned them. In 
some cases it is difficult to ascertain just what position an author takes 
concerning the theory for some of them use indiscriminately the terms 
hyparterial and eparterial in describing the tree. These terms, of course, 
may have only a simple topographical significance, as in the case with 
Huntington, without implying the meaning which Aeby attaches to 
them. Of all the authors who are considered as supporting Aeby’s 
theory His, alone, is outspoken in his belief that the eparterial bronchus 
is a dorsoventral bronchus which if it were in the hyparterial region 
would divide into dorsal and ventral branches. Willach, who first de- 
scribes the eparterial branch as arising from the first ventral bronchus, 
apparently accepts the theory, although Narath, a few years later advo- 
cating the same view, states that this single fact is sufficient to disprove 
Aeby’s hypothesis once and for all. Zumstein attacked the theory from 
another point of view, namely, by failing to find in corrosion specimens 
the relationship, which Aeby describes, and by noting variations in the 
pulmonary artery which, apparently, had no influence on the archi- 
tecture of the tree. In these observations Zumstein is supported by 
Narath, who also describes such specimens. Both observers also call 
attention to the fact that, at the time the primitive bronchi are formed, 
the pulmonary artery is a fine, delicate vessel which would have no in- 
fluence on the larger, firmer epithelial structures. Huntington attacks 
the theory from another point of view in looking upon the wandering 
of bronchi as the chief factor in the formation of the eparterial bronchi 
to which the relationship of the artery is simply secondary and topo- 
graphical. 
From the results recorded in this paper, it would appear that the rela- 
tionship of the arteries to the tree and the differentiation of two sets of 
bronchi with different relationships to the pulmonary arteries are pri- 
marily due to the topography of the anlage with respect to the Vena pul- 
monalis and the projection of the anlage ventralwards from the head gut. 
In consequence, the arteries form behind the primitive stems before any of 
the side branches are produced. Later the first lateral bronchus develops 
above and behind the artery, while the remainder of the series are formed 
below and in front of it. As the heart descends, the topography of the 
arteries to the stems changes, but in no way and at no time have the 
arteries a fundamental influence in differentiating two segments of the 
