Joseph Marshall Flint 59 
substituted for by inferior branches of Ventral 2 and partly by one of 
the branches of the first ventroinferior division of Lateral 4. On the 
left side, the ventroinferior divisions of Lateral 3 and Lateral 4. send 
branches to this region. Median 4 occurs on both sides opposite Lateral 4. 
It is particularly interesting to note the effect of the presence of median 
branches upon the dorsal series. Where median bronchi are present the 
median branches of the adjacent dorsal elements are very small and 
poorly developed, owing to the usurpation of their territory by this 
series. This naturally gives rise to the pictures which make it appear as 
though the median series might be transplanted elements from the dorsal 
bronchi. This relationship, however, is only another indication of the 
adaptability of the branches of the tree, for in this instance, had the 
median branches been suppressed, the median branches of the neighbor- 
ing dorsal series would have grown over to occupy the territory in which 
the former are found. 
In this specimen the ventral curvature of the lateral series is much 
more marked than in the preceding stage and now affects, to some ex- 
tent, the whole lateral series, although Lateral 5 bends slightly, while Lat- 
eral 2 (Pl. IV, Fig. 23) shows an extreme ventral curvature, a character- 
istic which is progressively diminished until Lateral 4 is reached. This 
unequal. bending has a marked effect on the stem bronchus and its other 
branches, and is responsible for the characteristic spiral-like insertion of 
the lateral and dorsal scries upon the stem of adult lungs which has been 
observed but not explained by most of the investigators since Aeby. As the 
lateral bronchi turn ventrally more rapidly in the upper than in the 
lower series, the stem bronchus and its branches twist with them. Thus 
in the adult lung Lateral 2 appears to rise on the ventrolateral aspect of 
the stem and each successive element of the lateral series is inserted 
shghtly more lateralwards. Similarly, on the adult tree, Dorsal 2 appears 
to originate somewhat on the dorsolateral surface of the stem, and the suc- 
ceeding elements are successively inserted more directly dorsalwards. ‘The 
spiral line connecting the origins of these two series of bronchi simply 
represent the degree of torsion of the stem bronchus as the lateral 
‘bronchi, in following the curvature of the chest wall, bend around the 
heart and liver. This is also nicely shown by the course of the pulmonary 
artery which, naturally, is mechanically influenced by the twisting of 
the stem bronchus as it is held in the angle formed between the laterai 
and dorsal series of bronchi. It is, of course, this secondary relation- 
ship of the lateral bronchi which led Aeby to term them ventral. In 
