44 The Development of the Lungs 
marked growth of its apical branch (PI. II, Figs. 17, 18, ap), which 
passes upwards and dorsalwards and terminates in two branches, one 
of which passes dorsally and inferior and indicates its first dorsal branch 
(Pl. II, Fig. 18, L. 2, d), while the other continues upwards as the 
extension of the stem of this bronchus. Near the extremity of L. 2 
another branch is given off, which extends ventralwards and inferior 
(Pl. II, Fig. 17, L. 2, vt). This corresponds to the ventroinferior 
division of the bronchus in the adult lung. As there is no ventral 
bronchus between L. 2 and L. 3 on the left side, the axial bronchus 
remains at this point perfectly smooth. The second dorsal bronchus 
(Pl. II, Fig. 18, D. 2) of this embryo is placed somewhat lower than the 
corresponding branch of the opposite series and arises just above the 
point where Lateral 3 originates. Like its homologue, it shows a subdivi- 
sion into two secondary branches, one of which is the regular medial 
branch (PI. I], Fig. D. 2, m), while the other forms the stem of Dorsal 2. 
Texr Hie. 14. 
TEXT Fic. 14. Section through the left lung of a pig 14.5 mm. long, showing 
the median evagination of the end bud to produce Medial 5. V= Ventral. 
D=Dorsal. M=Medial 5. S=lumen of end bud. 
The third lateral bronchus (Pl. I, Figs. 17, 18, L. 3) grows lateralwards 
and dorsalwards, and is not provided with secondary branches at this 
stage. Appearing as a small bud from the ventral aspect of the axial 
bronchus, a short distance above L. 4 is Ventral 3 (Pl. II, Fig. 17, V. 3), 
while at a point about opposite this branch and a little above, Dorsal 3 
(Pl. II, Fig. 18, D. 3) also originates as a small bud from the posterior 
surface of the stem bronchus, approximately midway between L. 3 and 
Lateral 4. The latter (Pl. II, Figs. 17, 18, L. 4) is somewhat shorter 
than the third, and has no secondary divisions. Ventral 4 (PI. I, Fig. 
17, V. +4) appears as a very faint swelling of the ventral aspect of the 
axial bronchus below L. 4+. In a corresponding position on the opposite 
side of the main bronchus Dorsal 4 appears (PI. II, Fig. 18, D. 4) also 
in the form of a slight evagination from the stem. Lateral 5 (PI. II, _ 
Fig. 17, L. 5) is merely indicated by a slight swelling on the side of the 
