42 The Development of the Lungs 
simply as a shght projection from the lateral wall of the axial bronchus 
as it continues downwards and ends in a terminal bud. The following is 
a tabulation of the tree in a pig of this age: 
TRACHEA. 
1, ale 
(2) DE: 
(2) VS. 
Right bronchus. Left bronchus. 
1.2: Ibe}, 
(2) DI. (2) Ap. 
(2) LI. (2) Gh: 
Were: 
1D} 2 D. 2 
ie Ibe & 
Weed Wee 
Drs Deo 
L. 4 L. 4 
15 
M. 5 
In a pig 15 mm. long (PI. I, Figs. 17 and 18) the trachea has in- 
creased in size and passes somewhat ventralwards to the point of bifurca- 
tion. On the right side and directed slightly dorsal and inferior, is Lat- 
eral 1 (Pl. II, Figs. 17 and 18, L. 1). A short distance from its point 
of origin, the ventral superior (Pl. II, Figs. 17, 18, vs) and dorsal in- 
ferior (Pl. II, Figs. 17, 18, di), branches are seen. These, in turn, now 
give rise to secondary branches. On the dorsal inferior branch, the first 
division (Pl. II, Fig. 18, d) is directed dorsally and somewhat medially 
This is the first main dorsal branch of the dorsoinferior in the adult lung, 
The other division continues on as the stem branch. The ventral superior 
bronchus passes laterally and superior. It now possesses a branch (PI. II, 
Fig. 18, d) passing dorsally and slightly upwards. This is the dorsal 
branch of the ventrosuperior division of L. 1, and is found usually in 
the adult lung. ‘The more general symmetry of the two main divisions of 
the trachea noted in the last reconstruction persists, the trachea passing 
downwards to the point of division and the right and left bronchi, as in 
the last stage, form with it a structure suggestive of a wish-bone. The 
axial bronchi bend laterally, dorsally, and medially, their point of widest 
divergence being now opposite the fourth lateral bronchi, a relation which 
persists in adult life, and with which the cesophagus, passing ventralwards 
at this level, probably has something to do. On either side, the second 
lateral bronchi pass lateralwards, then bend slightly dorsalwards and 
finally at their tips begin to bend ventralwards again. This indicates the 
