THE EMBRYOLOGY OF THE BIRD's LUNG 499 



great space required for the description of each branch, we have 

 undertaken to give merely a condensed account based on our 

 studies of metal casts. 



As shown in photographs of Wood's metal casts (figs. 44 and 

 45), the large divisions of the entobronchi are sread on the ven- 

 tral and mesial facets of the lung, and have already been gener- 

 ally described. 



The subdivisions of the ectobronchi occu})y most of the dorsal 

 surface except the central area of dorsobronchi. 



The entobronchi with their various ramifications form bron- 

 chial circuits of approximately the anterior one-third of the lung, 

 and of all that part which lies dorso-mesially to the central lung 

 tube (the cranial pente of Juillet) (figs. 44 and 45). In addition 

 to this, the transverse branch of the fourth entobronchus sup- 

 plies parabronchi for the middle region of the latero-ventral lung 

 facet. 



It is evident that the foiu" entobronchi are of wide distribution, 

 as the air passages arising from them occupy substantially one- 

 half of the lung, and they also give rise to three of the air-sacs. 



The superficial branches of the six ectobronchi, as already in- 

 dicated, anastomose with similar branches from the entobronchi 

 along the dorso-mesial border of the adult lung. There are also 

 internal branches that form parabronchi which unite at different 

 levels with those coming from entobronchi. A number of minor 

 ectobronchial branches extend laterally and anastomose, around 

 the reseau, with branches from the dorsobronchi. 



So far as we could determine the branches of the ectobronchi 

 do not exhibit a direct connection with any of the recurrent bron- 

 chi. There is, however, an indirect connection through the dorso- 

 bronchi, which anastomose on the one hand with ectobronchial 

 branches, and on the other hand, with twigs of the recurrent 

 bronchi from the posterior and abdominal air-sacs. 



Besides the connections indicated, the cephalad parabronchi of 

 the first ectobronchus also unite, through intermediation of 

 twigs from the dorsal branch of the second entobronchus. with 

 recurrent bronchi of the interclavicular air-sac. 



