PULMONARY EVOLUTION IN MAMMALIA 173 
For reasons to be considered subsequently the right lung is 
ordinarily, compared with the left, more favorably situated for 
further pulmonary extension in both the cranial and ventral 
areas of the newly acquired district of the ‘upper lobe.’ The 
points of origin of V!, supplying the ventral portion, and of its 
ascending branch, A, distributed to the cranial segment of the 
Figure 12 Figure 13 
Figs. 12 to 15 Diagrams illustrating the evolution of the eparterial bronchus 
in the mammalia. V‘-V!¥, ventro-lateral bronchi; A., ascending bronchus; 
D?-D*", dorsal bronchi; Hp., eparterial bronchus; U., upper lobe; M., middle 
lobe; Lst., lungstem. V!-V4, D1-D‘, V1-V7, D'-D?, Numerical order of ventro- 
lateral and dorsal bronchi after the eparterial bronchus has become established 
and functions as stembronchus for the newly acquired cranial pulmonary exten- 
sion. Cross-shaded: Archeal bronchial tree. Stippled: Components adapted to 
pulmonary extension craniad and neomorph eparterial bronchi with their anlagen. 
Black: Pulmonary artery. 
