38 The Development of the Lungs 
formed, in which case this area of the stem remains naked throughout 
life. This state of things, while occurring seldom, is found oftener on 
the right than on the left side and the cause may possibly be due, in this 
particular instance, to the presence of the rapidly growing Ventral 2, to- 
gether with the presence of L. 1 above, or otherwise simply to the general 
tendency for the tree to vary within wide limits. As in the case of the 
ventral and lateral group, the position of these dorsal buds may vary from 
complete suppression to a position on the stem at the level of L. 2, or to 
one opposite Lateral 3. The usual situation is about midway between the 
second and third lateral branches. These buds are the same as Narath’s 
Dorsal 2 and Aeby’s Dorsal 1. Our results agree with Aeby’s designation 
as Narath, in considering Lateral 1 and a dorsal branch, was forced ac- 
cordingly, to change the denomination of his dorsal series. Like Ventral 
2, I have designated the first dorsal bronchus as D. 2, simply to keep it 
in harmony with the lateral series. 
At this period the following branches of the bronchial tree have de- 
veloped: 
TRACHEA. 
1 ae 
Right stem bronchus. Left stem bronchus. 
Ibe Ibs 2 
Wind: : 
1D); 2 D. 2. 
Ibe, BF Ibe Bk 
13.5 mm. (Pl. II, Figs. 15, 16). At this stage the trachea is slightly 
larger and somewhat longer than in the preceding embryos. On its right 
side passing dorsolaterally is found L. 1 (Pl. II, Figs. 15, 16, L. 1) 
which has undergone division and yielded two practically equivalent 
branches, one of which passes downwards and dorsalwards (PI. II, Figs. 
15, 16 di) and the other lateralwards and slightly upwards (Pl. I, 
Figs. 15, 16 vs). These primary subdivisions, terminating in rounded 
buds, represent in the adult the dorsoinferior and the ventrosuperior 
branches of L. 1. At this stage, the two halves of the lung are much 
more symmetrical than we have seen them in any of the preceding recon- 
structions. The trachea and two main bronchi denuded of their side 
branches, now have more or less of a wish-bone shape. The trachea 
passes ventralwards to the origin of the stems and then, as the two axial 
bronchi diverge from the poiat of union, they also pass somewhat dorsally 
and reach their maximum point of separation at the level of the third 
lateral bronchi.. From this point, as the end buds are approached, they 
again converge towards the median line. The right is only slightly larger 
