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be reduplicated in a single interspace, but, in the pig, they never occur 
higher on the stem than the level of the fourth lateral bronchus. The 
reason for this fact lies in the presence of the oesophagus above this 
point, which allows no space for the development of medial elements 
from this portion of the stem bronchus. 
8. The following formula would represent the complete series of 
principal bronchi in the lung of the pig: 
Trachea. 
Lateral 1 
Right Stem Bronchus Left Stem Bronchus 
Lateral 2 Lateral 2 
Dorsal 2 Dorsal 2 
Ventral 2 
Lateral 3 Lateral 3 
Dorsal 3 Dorsal 3 
Ventral 3 Ventral 3 
Lateral 4 Lateral 4 
Dorsal 4 Dorsal 4 
Ventral 4 Ventral 4 
Medial 4 Medial 4 
Lateral 5 Lateral 5 
Dorsal 5 Dorsal 5 
Ventral 5 Ventral 5 
Medial 5 Medial 5 
Lateral 6 Lateral 6 
It is extremely rare to find a tree as complete as the one ex- 
pressed in this formula. A number of bronchi may be missing or 
else some may be reduplicated. 
9. The whole series of bronchi shows a most remarkable adaptation 
to the space in which they have to grow. This is true of both the 
chief bronchi as well as their smaller subdivisions. When, for example 
a bronchus is suppressed, an adjacent branch will grow into the area 
usually supplied by the missing element, substituting for its loss. It 
is in this way that we obtain the large series of pictures which sug- 
gest a wandering of the secondary branches from the lateral and dorsal 
elements on to the stem bronchus. After a careful study of this point, 
it may be definitely stated that bronchi never wander. They remain 
firmly fixed on the stem or side branches where they originate. Not 
uncommonly their direction may be altered, however, by changes in 
the space in which they develop. 
