Joseph Marshall Flint 41 
dred lungs, do they occur higher than a short distance above the level of 
Lateral 4. They may exist only on one side or else on both. Like the 
other series, they arise as lateral outgrowths of the bronchial stem, not as 
secondary derivations of the dorsal series, according to the processes de- 
scribed by either Narath or Robinson. It is interesting, moreover, to note 
the relation of this group to the cesophagus. In the higher levels where 
the cesophagus lies between the stem bronchi, no medial bronchi occur, in 
the lower levels, however, as the cesophagus passes ventralwards to the 
stems, leaving the medial surfaces of the lung free, these branches are 
produced. Text Fig. 26 shows these conditions well. The edge of the 
cesophagus is seen in cross-section, while from the median wall of the end 
bud below it an evagination which will form a Medial 4 or 5 is clearly 
seen (Fig. 26M). This would seem to indicate another adaptation on 
the part of the tree, to its space relationships. 
On the left side, L. 2 (Pl. II, Figs. 15, 16, L. 2) is directed lateral- 
wards and slightly dorsalwards. Like the corresponding bronchus on 
the right side, there has been a dichotomous division, which has yielded 
two branches, one directed dorsally and superior (PI. II, Figs. 15, 16 ap) 
and the other lateral and ventral. The latter is the continuation of the 
main bronchus, while the former constitutes the apical branch, or 
Bronchus ascendens of His, of L. 2 on the left side. Owing to the 
unobstructed possibility of its growth upwards, inasmuch as there is on 
the left side no L. 1, this branch, as we have seen, grows in a slightly dif- 
ferent direction from the corresponding division of the same lateral 
bronchus on the right side, but, for the reasons given above, it must be 
viewed as distinctly homologous with the dorsoinferior branch of right 
L. 2. This branch and its relationships may be seen in many of Narath’s 
illustrations, from which the nature of its origin is as clearly shown as 
in the pig’s lung. On the left side, there is no V. 2, but between L. 2 
and L. 3, the Dorsal 2 (Pl. II, Fig. 16, D. 2), which already appeared 
in the earlier stages, is now well marked. 
Lateral 3 (Pl. I, Figs. 15, 16, L. 3) is directed laterally and possesses 
a distinct bud at the end. It is also directed slightly dorsalwards, occu- 
pying a plane almost identical with the second lateral branch above. On 
the ventral surface of the axial bronchus, just below the point of origin 
of the third lateral, a small projection indicates V. 3 (PI. II, Fig. 15, 
V. 3), while behind the stem bronchus, but somewhat lower, a similar 
projection marks the origin of the D. 3 (Pl. II, Fig. 16, D. 3). The 
fourth lateral bronchus (Pl. I], Figs. 15, 16, L. 4) exists at this stage 
