48 The Development of the Lungs 
Ventral 2, the infracardiae bronchus, has grown markedly, and presents 
a long inferior branch (PI. I, Fig. 19, V. 2, 7), which passes downwards 
and ventralwards and is indicated in the architectural history of the 
younger stages. The next division is a small bud from the upper por- 
tion of V. 2. (Pl. IL, Kiss 19) V2 2) us) which has a yentrosupenor 
direction and is found in specimens of the adult tree. This branch is 
small and at this stage consists simply of a shghtly marked bud from 
the main bronchus. In most of the corrosions I have made of the lungs 
of older embryos it always shows by its flattened spreading branching that 
it is more or less influenced by the presence of the heart above it. The 
ventroinferior branch (Pl. II, Fig. 19, V. 2, vt), which is the next in 
order, is a slight bud, passing downwards and slightly ventralwards, and 
which, it may be worth while observing, with the inferior branch, some- 
times substitutes for Ventral 3, when it is suppressed. After this branch, 
the main bronchus continues on to terminate in slight end swelling. 
Here we are able to observe again the mechanical influence of environ- 
ment on the growth of a bronchus. The inferior group of branches of 
Ventral 2 have space in which to grow and are accordingly of exaggerated 
size in comparison with the superior group, which cannot attain such ex- 
tensive development, owing to the presence of the heart above them. In 
this bronchus, as well as in the laterals, we also have the possibility of 
propagation of the stem through either branch of a dichotomous division, 
as I have a number of specimens on which the ventrosuperior division 
arises before the inferior, indicating in these specimens, the use of the 
latter as the stem with the inferior branch arising from a subsequent 
forking. Right Dorsal 2 (Pl. III, Fig. 20, D. 2) of this specimen has 
not developed as far as the corresponding bronchus in the preceding stage, 
the terminal bud merely suggesting an approaching division, which was 
already well advanced in the bronchial tree from a 15 mm. pig. Such 
variations, however, are not uncommon. ‘The third lateral bronchus (PI. 
II, Fig. 19; Pl. III, Fig. 20, L. 3) passes outwards and slightly ventral- 
wards. From its dorsal aspect, a dorsal branch (PI. I], Fig. 19; Pl. III, 
Fig. 20, L. 3, d) originates, which terminates in the swelling already 
showing signs of division. The third ventral bronchus (PI. I, Fig. 19, 
V. 3) arises from the ventral aspect of the stem, between Lateral 3 and 4 
and grows downwards, apparently influenced by the marked development 
of Ventral 2 above it. Dorsal 3 (PI. III, Fig. 20, D. 3), passes dorsal- 
wards and lateralwards, and has a well-marked median branch (PI. III, 
Fig. 20, D. 3, m) which terminates in a large bud, while the main 
bronchus points somewhat dorsally and laterally. Lateral 4 (Pl. II, 
