Joseph Marshall Flint 125 
8. The following formula would represent the complete series of prin- 
cipal 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. 
Ventrai 5. Ventral 5. 
Medial 5. Medial 5. 
Lateral 6. Lateral 6. 
It is extremely rare to find a tree as complete as the one expressed in 
this formula. A number of bronchi may be missing or else some may be 
reduplicated. 
9. The whole series of bronchi show 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 suggest a 
wandering of the secondary branches from the lateral and dorsal ele- 
ments 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 uncom- 
monly their direction may be altered, however, by changes in the space 
in which they develop. 
This response on the part of the growing bronchi to their space rela- 
tionships is also shown in the course or direction of the principal elements 
as well as their secondary branches. We have, therefore, Lateral 1 
produced and growing into the area between the upper part of the heart 
and chest wall. Owing to the larger space just beside the vertebral 
column and the antagonism between it and Lateral 2, the lower branches 
of Lateral 1 are forced dorsalwards until it resembles superficially a 
