Joseph Marshall Flint 83 
bronchi to their environment, or the possible influence of environment 
upon the branches of the tree. The tips of the Lobus medius have 
grown around the heart until they have almost met in the midline. On 
the undersurface, the unpaired Lobus infracardiacus (Fig. 20, V. 2) 
is clearly seen particularly in its relationship to the Vena cava inferior. 
With the increase in size between this and the last stage, the swellings 
over the various bronchi have disappeared and the surface of the lobes 
become smooth. The topography of the Lobus inferior on both dia- 
phragmatic and lateral surfaces is indicated on the surface of the lungs 
by dotted lines. By a comparison with Fig. 19, the origin of these 
topographical relations are clear. 
With the further development of the pig’s lung which has been de- 
scribed by Narath, I cannot agree. In the account of the form relation- 
ships, his work is accurate, but in the interpretation of the relative sig- 
nificance of the different parts of the lung and the equivalent values of 
the lobes on each side, our results differ chiefly with our derivation of the 
principal bronchi. That is to say, according to his view the Lobus 
superior and the Lobus medius on the right side are equivalent to the 
Lobus superior on the left. They are almost or completely separated 
through an accessory fissure, making the Lobus superior correspond to 
the dorsal or apical area in his preparations and equivalent to the cephalic 
or apical projection of the Lobus superior of the left lung. The latter, 
as we have seen, is only a secondary substitution product of a branch 
of left L. 2, ontogenetically equivalent to the region of the Lobus medius 
on the right side which is supplied by the large dorsoinferior bronchus. 
On the other hand, the right Lobus superior, supplied by L. 1, is totally 
unrepresented in the left lung. This unpaired lobe, therefore, and also 
the cephalic portion of the upper lobe on the left, properly belong not to 
the dorsal area, as Narath suggests, but to our lateral and his ventral 
region. The fissure between Lobus superior and Lobus medius on 
the right would be primary and not accessory in the sense of Narath. 
In recapitulating the development of the lobes, we may say, then. that 
the mesodermic portion of the lungs, derived from the general mesoderm 
about the head gut, is pushed out by the growing bronchi to form 
irregular asymmetrical swellings in the coelom. These are the anlagen 
of the primitive wings of the lungs. With the appearance of L. 1 on 
‘the right side of the trachea, and L. 2 on each stem bronchus, primary 
swellings are formed in the two wings over these bronchi, giving rise to 
the simplest form of the Lobus superior, Lobus medius on the right side, 
and the Lobus superior on the left. The remainder of the mesoderm 
