46 The Development of the Lungs 
Fig. 20, L. 1, vs) branches. The dorsoinferior passes downwards and 
dorsalwards and terminates in the neighborhood of D. 2, a relationship 
which persists to the adult stage as its further growth downwards is now 
checked by the series of dorsal bronchi below. This branch shows new 
divisions over the preceding stage as we find besides the dorsal branch, 
which passes dorsalwards and medialward, a lateral branch (PI. III, 
Fg. 20, 1) arising about the same level, which passes laterally and dor- 
sally. Both of these divisions terminate in end buds. The main stem 
of the bronchus continues downwards to its termination, which is marked 
by slight end swelling. The ventrosuperior or apical branch (Pl. U1, 
Fig. 19; Pl. III, Fig. 20, vs) of L. 1, extends further cephalad than in 
the earlier stages. Besides the dorsal branch indicated in the preceding 
reconstruction, which shows signs of division, a lateroinferior branch 
(Pl. II, Fig. 19; Pl. III, Fig. 20, 1) is given off somewhat further on, 
which passes at this time downwards and shghtly outwards, and forms 
the first lateroinferior branch on this bronchus of the adult tree. The 
main stem continues upwards and ends in a terminal bud. The trachea 
and the stem bronchi still preserve the characteristic wish-bone appear- 
ance noted in the two preceding reconstructions. The two axial bronchi 
bending lateralwards, dorsalwards, and medialwards, the point of widest 
separation being, as in the earlier stages, about the level of the fourth 
lateral bronchi. In the preceding reconstruction, the beginning of the 
ventral growth of the two wings of the lung were apparent on Lateral 2. 
This action is now also shown on the third lateral branches. The first 
pair, however, curve around the heart, while those of the lower series 
follow the chest wall and the curvature of the diaphragm over the 
liver. The fourth, fifth, and sixth lateral divisions still pass outwards 
and slightly backwards without showing this bending at the extremities. - 
On the right side, the second lateral bronchus arises about the point of 
bifurcation of the trachea, and passes slightly ventralwards, then runs 
upwards, slightly dorsalwards, and again ventralwards, preserving its 
course practically in one horizontal plane. In this specimen the first 
branch is a ventroinferior (Pl. IJ; Fig. 19, L.2, vt), which extends 
downwards and ends in a bud, while the dorsoinferior branch (Pl. II, 
Fig. 19; Pl. Ill, Fig. 20, L.2, dv), which is scarcely larger than the 
preceding stage, is the second branch of Lateral 2. This condition indi- 
cates one of the very important factors in the growth of the bronchi, 
namely the ability of either branch after a division to continue on as a 
stem. In nine out of ten cases, the ventral fork, after the first division 
of Lateral 2, produces the main trunk, leaving the dorsal fork as the large 
