491 



The recurrent bronchi of the other three air-sacs anastomose 

 during the fifteenth day in a similar manner with parabronchi in the 

 parts of the lung adjacent to them. It results that the anterior inter- 

 mediate sac comes into communication with the air passages in the 

 lateroventral lung region and the sub-bronchial sac comes into communi- 

 cation with passages in the anterior part of the lung. 



The anastomosing twigs are at first very slender but by the 

 eighteenth day of incubation have increased in diameter so as to be 

 practically the same size as the branches which they connect. The 



r. br.t 1 

 d.o'.a.b. 



djo.'p. i. 



r hr l-ät. 3 \ 'best. 

 laU 2 



par 



Fig. 7. Diagram of lateral side of right lung of embryo of fifteen day stage, 

 to show the recurrent bronchi {r.br.) of the posterior intermediate and abdominal 

 air-sacs. The outlines of the recurrent bronchi themselves, so far as represented, 

 were traced with the aid of the camera lucida from an air-injected preparation. Dotted 

 portion diagrammatic. Reference letters as before. 



recurrent bronchi have by the eighteenth day of development assumed 

 the relations to other parts of the bronchial tree which they bear in 

 the adult lung. 



Transition to the Adult. 

 In showing how the adult condition is reached it will be advanta- 

 geous to summarize the principal changes after the eleventh day. 

 As already stated, the sacs expand more rapidly after this stage. This 

 is especially true of the more posterior ones. 



