12 The Development of the Lungs 
thus giving to us three principal forms to the bronchial tree, namely, (1) 
Lungs with an eparterial system on both sides; (2) Lungs with an epar- 
terial system on the right side; (3) Lungs without an eparterial system. 
In some instances the eparterial bronchus is shifted back on to the trachea 
while in certain lower animals, especially the birds and reptiles, the 
eparterial system is more highly developed than in mammals. In the 
phylogeny of the lung, however, it becomes smaller until it may dis- 
appear entirely in some of the higher series. 
In the further development of the lung sacs in the human embryo as 
described by His, 87, all secondary bronchi arise from the first five 
primary divisions. Three of these occur on the right lung sac and two 
on the left. On the right side they are termed upper, middle, and end 
buds while those on the left are respectively lateral and end buds. With 
Aeby, His finds the primitive lungs prismatic in transection with one 
attached and two free angles between which lies its dorsal or costal sur- 
face. The stems give rise to the so-called ventral bronchi, which, His be- 
lieves, should have been termed lateral bronchi. Owing, however, to the 
general acceptance of Aeby’s nomenclature, he has followed it. From 
the stem bronchus dorsal branches appear which like the ventral group 
subdivide regularly. These secondary branches are accordingly desig- 
nated as follows: 
1. Bronchus dorsalis posterior. 
. Bronchus dorsalis lateralis. 
. Bronchus ventralis lateralis. 
. Bronchus ventralis anterior. 
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His agrees with Aeby with reference to the interpretation of the epar- 
terial bronchus and looks upon it as an unpaired branch which, if it were 
in the hyparterial region, would divide into dorsal and ventral elements. 
As a matter of fact, after its appearance in the human embryo, it gives — 
off branches which have these two general directions. On the other 
hand, he looks upon the Bronchus cardiacus as a true side bronchus, 
which, in opposition to the dorsal series, passes in a ventral direction. 
Its independence is shown in its early appearance as well as by the dis- 
tance which separates it from the first and second ventral bronchi. It is 
regarded by His as an element which appears out of the schematic order 
and follows its own development. In the left lung, cardiac and eparterial 
bronchi are lacking, but the first ventral bronchus sends up a strong 
dorsal branch, which mounts up into the apical region of the left lung 
and is designated the Bronchus ascendens. In this way a substitution is 
made for the eparterial bronchus of the right side which, with the 
