60 The Development of the Lungs 
their origin, however, they are, as we have seen, distinctly lateral, and I 
have applied to them, therefore, the genetic nomenclature. 
The condition of the tfee a few days after birth is shown in PI. IV, 
Fig. 25. In order to show the three chief series of bronchi in a single 
illustration, Ventral 2, the Bronchus infracardiacus, has been broken off 
near the root. The tip of the ventrosuperior branch of the tracheal bron- 
chus, owing to an accident, was also broken and should extend upwards 
and ventralwards for a considerable distance. Although the general form 
of the tree has not changed to any marked extent, besides the increase in 
the branching, the second laterals extend far ventralwards so as to em- 
brace the heart. The effect of the presence of the heart on the tree, as 
in earlier stages, is shown particularly well by the direction of the 
branches of the tracheal and second lateral branches. The portions of 
these bronchi, which come in relation to the heart are nude, their 
branches extend so as to occupy the remainder of the chest cavity in their 
neighborhood, a relationship, which may also be seen by an inspection of 
the tables in the younger stages. Below Lateral 2, however, owing to a 
freer environment, the bronchi show the power of branching in any 
direction. In this specimen a few interesting variations are shown, one 
of which is of particular importance for comparison with the conditions 
shown in the preceding stage, namely, in the presence of seven lateral 
bronchi on the right side and five on the left. On the right side the 
whole ventral series is present, while on the left, two ventral bronchi 
occur between Lateral 5 and Lateral 6, a fact which would be difficult to 
explain if we viewed these branches as derivations of the lateral series 
since the entire group is complete from Ventral 3 down. Dorsal 3 on the 
right side is hyperdeveloped, while Dorsal 4 is quite small, a not unusual 
variation. None of my other specimens show such a marked aevelop- 
ment of the medial bronchi as Medial 4, 5, and 6, present on the right 
side, as well as an element of this series opposite Lateral 5 on the left side. 
RELATIONS OF THE BLOOD-VESSELS TO THE BRONCHIAL TREE. 
In tracing the angiogenesis of the vascular system in the submaxillary 
gland and the suprarenal body, the author, 00, 02, 03, showed that some 
of the mechanical principles, which Thoma, 93, in his well-known re- 
searches found were involved in the development of the blood-vessels in 
the Area vasculosa of the chick, might be applied to vascular systems 
developing in three dimensions in the growing organs of mammals. 
Thoma found in the chick, that arteries and veins are originally simple 
capillaries. The subsequent transformation of the latter into arteries 
