Joseph Marshall Flint 49 
Fig. 19; Pl. III, Fig. 20, L. 4) has a definite ventral bud and at its 
ends is undergoing division. The fourth ventral bronchus (Pl. II, 
Fig. 19, V. 4) is somewhat smaller than the V. 3, and appears as a 
constricted button-like bud from the ventral aspect of the axial trunk, 
while Dorsal 4, arising at a somewhat higher level on the opposite side of 
the stem ends in a relatively large bud, which is as yet undivided. From 
the lateral aspect of the axial bronchus Lateral 5 (Pl. I], Fig. 19; Pl. III, 
Fig. 20, L. 5) takes origin, and ends in a terminal bud without division. 
D. 5 (Pl. Ill, Fig. 20, D. 5) is the smallest of the dorsal branches 
on this side, and appears simply a pedunculated projection from the 
dorsal aspect of the main stem, while the fifth ventral bronchus is present 
solely as a slight elevation or projection (Pl. II, Fig. 19, V. 5) from 
the ventral wall of the axial bronchus which, continuing caudalwards, 
ends in a terminal bud. 
On the left side Lateral 2 (PI. II, Fig. 19; Pl. III, Fig. 20, L. 2), which 
was practically symmetrical with the corresponding branch on the right 
side in a pig 13.5 mm. long has now, in the rapid development of its 
main branch, lost even more than in the preceding stage its symmetrical 
relationships with right L.2. The ventrosuperior or apical branch (PI. 
II, Fig. 19; Pl. III, Fig. 20, L. 2, ap) is markedly increased in size, 
and now arises from the more superior aspect of the bronchus and passes 
superiorly and slightly dorsalwards. Its termination has reached a 
height equal to the point of origin of the tracheal bronchus on the right 
side. From its dorsal aspect, the first dorsal branch (PI. III, Fig. 20, 
L. 2, d) is derived, which is now subdivided into two regular buds. A 
little higher, the lateral branch (PI. III, Fig. 20, L. 2, 1) is seen, while 
the apical end of the bronchus is in the stage of division. Further lateral- 
wards, on L. 2 a dorsosuperior branch (PI. III, Fig. 20, L. 2, ds) origi- 
nates, which has a marked bud and is in process of division, while the 
next is an inferior or ventroinferior branch (Pl. II, Fig. 19; Pl. III, 
Fig. 20, L. 2, vt) existing simply as a small pedunculated projection from 
the under surface of the bronchus. Lateral 2 terminates in a bud, which 
has undergone definite division, but the resulting branches are not yet 
sufficiently characteristic to be placed with reference to the adult tree. 
Inasmuch as Ventral 2 on the left side is always missing on the pig’s 
lung, that aspect of the main bronchus remains perfectly smooth. At this 
period, however, the Vena pulmonalis already overlies this portion of the 
axial stem, but, for the sake of clearness in the illustration, it has been 
placed in approximately the median plane. Dorsal 2 (Pl. III, Fig. 20, 
D. 2) arising just above L. 3 passes dorsalwards, and has two marked 
4 
