36 The Development of the Lungs 
a level below the point where the stem bronchus has already regained its 
cylindrical form after the production of the second lateral bronchus on the 
right side. Of the possibility of its being a branch of Lateral 2, in these 
specimens, there is not the shghtest evidence. In this particular lung, D. 
2 and V. 2 are given off at practically the same level. This is, however, 
not always the case as one, usually the ventral, may arise higher up. 
It is this variability in the origin of these branches which gives rise in 
the adult tree to the series of stages, which simulate a transplantation 
of the Ventral 2 from Lateral 2 to the stem bronchus. They represent, 
however, simply a normal range of variation in the origin of the bronchus. 
Narath states the wax-plate method is not adapted to the study of these 
branches and has, for the most part, used specimens cleared in oil of cloves. 
In my experience, the latter method is valuable only for the lateral bronchi 
where the buds are seen in profile and, therefore, are sharply outlined. 
In such specimens, either the dorsal or the ventral series must be studied 
not only through the mesoderm, but also through the entire thickness of 
the stem bronchus. In looking upon the surfaces of such buds as D. 2 
and V. 2 in an embryo like that represented in Pl. I, Figs. 11 and 12, 
the slight projections forming the anlagen of these branches are invisible 
because they cannot be studied in contour. After they have developed 
into well-formed buds, they are quite apparent in cleared preparations, 
particularly when the stereoscopic microscope is used. By that time, how- 
ever, the important stages of their origin are lost. So far as is known 
to me, reconstructions, controlled and supplemented by cleared and dis- 
sected specimens afford us the only opportunity to see the first traces 
of these branches. For such schematic pictures as shown by Narath, 
96 (Text Figs. 1, 2, 3), which represent schemata of the origin of his 
apical bronchus and V. 2 from the bud of L. 2, I can find, in the pig, no 
parallel. Furthermore, the bud of V. 2 is shown in the schemata before 
the apical bronchus appears, while in the pig the latter is either the 
independent precursor or the contemporary of Lateral 2, while Ventral 
2 is not formed until after the other two branches are well developed. 
At this stage the following divisions have appeared in the primitive 
bronchial tree: 
TRACHEA. 
Lateral 1. 
Right stem bronchus. Left stem bronchus. 
15 Py. Mee 
WVa2e 
IDE 
In a reconstruction of the bronchial tree of a pig 12 mm. (PI. I, 
Figs. 13, 14) the trachea and stem bronchi have increased considerably 
