THE EMBRYOLOGY OF THE BIRD's LUNG 481 



Campana ('75) 'bronches secondaires externes.' Although they 

 do not attain in the adult lung the dimensions of ento- and ecto- 

 bronchi they are, nevertheless, coordinate with them (1) in that 

 they arise directly from the central lung tube; (2) that they are 

 the principal branches supplying the lateral part of the ung; 

 (3) that they make their appearance about the same time as ec- 

 tobronchi. Accordingly the term laterobronchi (lateribronchi, 

 Schulze) seems appropriate. 



The first three laterobronchi are illustrated in figure 32, lat. 

 1, 2, 3. Subsequently three smaller ones arise caudad to the 

 anterior three making a total of six laterobronchi. 



Other relatively small bronchi, somewhat more dorsal in posi- 

 tion, arise similarly, but at a later stage. These correspond to 

 Campana's fourth kind of secondary bronchi and we have called 

 them dorsobronchi (dorsilateribronchi of Schulze). Descrip- 

 tions of the numerous dorsobronchi and of the six laterobronchi 

 will be taken up later. 



Attention may be briefly directed to the configuration of the 

 central lung tube. It forms a figure resembling an elongated 

 S, the posterior bend of which is more marked. The terminal 

 end is inflated and projects into a protuberance of mesenchymal 

 tissue, and form the primordium of the abdominal air-sac. 

 The central expanded part is the embryonic vestibulum. As in- 

 dicated above, the embryonic vestibulum is not to be confused 

 with that of the adult. 



The bronchial tree from this stage on, continues to grow and 

 its branches to ramify so profusely, that for the sake of clearness 

 it is necessary to describe its subsequent development under 

 separate headings. 



The entobronchi. As noted above, the first entobronchus makes 

 its appearance early on the sixth da}^ of development as a papil- 

 late bud from the dorsal wall of the anterior division of the meso- 

 bronchus (mesial in the adult lung). In order to maintain a 

 correct orientation the following should be noted. Beginning 

 late on the ninth day the lungs begin to rotate about their longi- 

 tudinal axis and pass through an angle of about 30 degrees be- 

 fore reaching their adult position. This rotation carries the 



