144 HUSTINGTON. 



We can recognize two main trunks on each side, one cephalic, 

 the other caudal. The cephalic trunk supplies the anterior and 

 middle portion of the lung, the main migratory modifications in 

 the different types taking place within its region of distribution. 



The caudal trunk supplies the posterior and larger portion of 

 the lung. 



In the subsequent development of the stem-bronchus and its 

 monopodic type of branching, characteristic of the majority of 

 mammalian lungs, the following factors are active : 



a. Complete segmentation of the tracheal bulla, producing 

 the usual bifurcation. This establishes the proximal portion of 

 the ** stem-bronchus," and gives to the cephalic primary trunk 

 A the position of a lateral branch derived from the same. 



b. The caudal continuation of the stem-bronchus is composed 

 of the primary caudal trunk B and its medial secondary branch 

 B" , the lateral branch B' and subsequently developing lateral 

 accessory branches appearing as the " ventral branches of the 

 stem-bronchus" (Aeby). 



c. The cardiac bronchus usually appears as a special acces- 

 sory branch derived from the stem-bronchus of the right side 

 only (exception vide supra, Auchenid). 



10. In the majority of forms examined the pulmonary artery 

 is not dorsal to the stem-bronchus, except in the terminal part. 

 The position, as Narath has pointed out, is lateral or dorso- 

 lateral. 



11. Hence, the distinction into "dorsal" and "ventral" 

 branches, separated by the pulmonary artery, should be aban- 

 doned. 



12. It will be seen that our results asrree with the conclusions 

 reached by Narath in regard to the equivalence of the anterior 

 or cephalic branches of right and left side in a symmetrical lungs. 

 We differ from him in our interpretation of the derivation of the 

 ''apical bronchus" which he regards as the dorsal branch of the 

 first ventral bronchus. 



We differ also as regards the above outlined phylogenetic de- 

 velopment of the "stem-bronchus" and its monopodic system 

 of branching. 



