Joseph Marshall Flint 105 
Later still when the total volume of the lung is such that each bronchus 
is more or less equally surrounded by mesoderm, the dichotomy is equal, 
although of the two forks resulting from a division, one becomes the 
stem and the other is shunted off as a side branch. The point, however, 
where monopody ceases and dichotomy begins is apparently different in 
different species and may be different in different parts of the lung. In 
the pig it is below Lateral 6 while, in man, according to His, the transfer 
is made at Lateral 4. It must be remembered in this connection, how- 
ever, that the space relations in this region of the human lung are quite 
different from those in the pig owing to the different position of the 
heart, diaphragm, and liver. 
The bronchi, apparently, show great adaptability both in the power 
and direction of their growth. This interesting characteristic is best 
shown when one of the chief bronchi are suppressed. Adjacent branches, 
while still rooted firmly at their point of origin, then grow into the area 
of the lung usually supplied by the suppressed element, a process which, 
taken in connection with the extreme variation of the point of origin of 
the bronchi, give rise, in the adult tree, to the series of pictures which 
suggest a wandering of the branches. In my whole series of specimens 
numbering ten reconstructions and many cleared specimens 3 to 18.5 
mm., and about 100 corrosions of pigs from 4 cm. to the half-grown 
stage, I have never found any evidence which pointed to a wandering of 
any elements of the tree. The bronchi remain attached to their stems 
where they are formed, although their branching is controlled to a great 
extent by the space in which they have to grow. When this is altered 
by the suppression of one of the usual elements, adjacent branches show 
a power of substitution which is perhaps best exemplified in the fate of 
the two dorsal forks of the first division of the right and left Lateral 2. 
On the right side, this branch, owing to the presence of the Lateral 1 
above it, is forced to grow downwards and posterior to form a dorso- 
inferior branch of Lateral 2, while on the left side, this same fork, un- 
obstructed by the absence of Lateral 1, grows upwards to substitute for 
the suppression of the lateral element above. 
In turning to the literature we find that between such outspoken de- 
scriptions as those of d’Hardiviller for example, on the one hand, and 
Justesen, on the other, it is not difficult to differentiate, but in the cases 
where terms like sympodial dichotomy and monopody with acropetal 
development of the lateral buds are used, it is not always easy to deter- 
mine whether the authors have not been describing the same process with 
different words. At the outset, therefore, it may be well to state that 
