PULMONARY EVOLUTION IN MAMMALIA 141 
the primary bronchial derivatives from the moment of their first 
appearance laid down in a ventral and a dorsal (respectively 
lateral and medial) row (cf. 1. c., Taf. 27, Figs. 23 and 24). He 
adds that the dorsal as well as the ventral branches arise quite 
unmistakably as separate primary outgrowths from the stem. 
He concludes with the statement “‘Ich glaube nicht, dass die 
komparative Lungenanatomie fiir die von Narath ausgesprochene 
Ansicht eine Stiitze bietet.”’ 
It is clear that the details of the comparative and ontogenetic 
evidence call for critical analysis on the basis of the two main 
assumptions associated in the migratory theory: 
1. that the dorsal bronchi are primarily derived from the ven- 
tral series; 
2. that the eparterial bronchus, when it appears as such, is 
the most cranial member of the dorsal series, hence, like the rest, 
primarily a derivative of its corresponding ventral associate. 
These two basic propositions suggest the following 
considerations: 
1. By reason of their importance to the migratory theory 
Narath paid special attention to the main and accessory dorsal 
bronchi. A summary of the morphological characters which 
they may present can be schematized in figure 5, in which the 
dorsal bronchus belonging to a given segment of the stembronchus 
is indicated as D*, and the ventral bronchus to which it is genet- 
ically related according to the migratory theory as V”, while V~ 
represents the next cranial ventral bronchus. 
1. D* may arise from the stembronchus opposite to V“ on the 
same level with it. 
2. D* may arise at a higher level than its ventral associate 
V7, at any point of the stembronchus in the segment V7-V”. 
3. D* may ascend to the level of the ventral bronchus next 
above, V*. 
4. D* may advance craniad above this level. 
5. The origin of D* may be depressed further caudad, below 
the level of V”. 
6. D* may arise from the lateral surface of the stembronchus, 
close to V”. 
