25 
2. The first lateral bronchus, the so-called „eparterial bronchus“, 
is, in the pig, unpaired and arises as a lateral outgrowth from the 
right side of the trachea, just above the roots of the two stem bronchi. 
It is distinctly lateral in origin and bears a serial relationship to the 
remainder of the lateral bronchi. Its position in mammals varies, 
sometimes it is on the stem bronchus, but it is often situated on the 
trachea. This difference can usually be explained by the point of 
origin of the two stem bronchi with reference to the pair designated 
as Lateral 2. If the stems originate low down, then Lateral 1 is 
thrown on to the trachea, while if their origin is higher up, the first 
Lateral arises from the stem bronchus. Apparently Lateral 1 is 
characteristic of mammals. A bronchus corresponding to it has not 
been found either in reptilia or amphibia. In almost all mammals it 
is an unpaired element. No satisfactory proof has ever been brought 
to show a bilateral development of Lateral 1 with a subsequent de- 
generation of the left bronchus, notwithstanding the fact that this 
process has been described in two species. At no time in the life 
history of the pig is there a Lateral 1 formed on the left side. There 
is, furthermore, no embryological evidence to show a relationship be- 
tween Lateral 1 and the dorsal series of bronchi. These characteristics 
are secondary and result from the antagonistic effects of the growth of 
Lateral 1 and Lateral 2. The latter is forced somewhat ventralwards, 
while the former is pressed dorsalwards, until its lower branches lie 
above the dorsal series of bronchi. 
3. The remainder of the lateral series originate in succession from 
the lateral side of the stem bronchus as lateral outgrowths or hernia 
like expansions of the wall of the stem bronchus near the terminal 
bud. These elements in their growth outwards finally reach the chest 
wall. Here they are compelled to grow in the space between the ribs 
and the liver and consequently follow the curvature of the chest wall 
which ultimately gives them, more or less, the appearance of ventral 
bronchi, a fact which led Aeby, who studied only the finished tree, to 
call them the ventral series. 
4. The dorsal series of bronchi, originating like the lateral group 
as outgrowth from the stem bronchus, are usually paired. They alter- 
uate with the paired lateral bronchi and are independent productions 
of the stem. They do not either ontogenetically or phylogenetically 
originate from the lateral bronchi. For convenience, the first pair are 
called Dorsal 2, to keep the designation harmonious with the larger 
series of lateral bronchi. 
5. The ventral bronchi originate as outgrowths from the ventral 
