THE KMBKYOLOGY OF THE BIKD's LUNG 19 



the lateral moiety of this sac has its origin. The recurrent ori- 

 fices are three or four in number, and are the proximal openings 

 of the recurrent bronchi. Reference to figure 47 will show that 

 on the eleventh day of incubation there were but two recurrent 

 openings connected with the sac. The change to the adult con- 

 dition is brought about by the extension of the proximal ends of 

 the original recurrent bronchial buds. 



Juillet insists that there is no direct connection of the inter- 

 clavicular with the first entobroncus, and accordingly, classifies 

 this lateral group of orifices as simple polybronchial. We con- 

 clude, however, that the group is a mixed polybronchial and will 

 return to the question under our general considerations. 



The anterior intermediate air-sac also has two groups of ori- 

 fices. The monobronchial direct orifice (figs. 47, 54) has already 

 been mentioned in connection with the corresponding orifice of 

 the interclavicular air sac. The other and more ventral group is 

 of the polybronchial recurrent type. The number of orifices 

 varies, but is usuall five or six. 



The posterior intermediate sac communicates with the lung 

 by a polybronchial group of orifices made up of both direct and 

 recurrent tubes (polybronchial mixed). There is one direct ori- 

 fice (figs. 53, 54), which is the opening of the third laterobronchus 

 from which this sac has its origin. The recurrent orifices (figs. 

 53) represent the lungs of a one-day chick, but the relation of 

 the orifices is the same as in the adult lung), three or four in 

 number, as the openings of the recurrent bronchi and have a 

 history very similar to that already described in connection with 

 the two preceding sacs. The anterior ends of the posterior in- 

 termediate recurrent bronchi have for the most part anastomosed 

 with the first and second laterobronchi. 



The orifices of the abdominal air-sac are also of two kinds, di- 

 rect and recurrent, which are so arranged as to form a mixed 

 polybronchial group. The direct orifice (figs. 53 and 54) is the 

 opening of the mesobronchus into the sac. The recurrent ori- 

 fices arising as previously described are four or five in number. 

 Schulze has shown that variations as to number exist in different 

 birds being six to nine and sometimes reduced to one. 



