2 WILLIAM A. LOCY AND OLOF LARSELL 



'10) and Juillet ('12) who, working independently, and without 

 knowledge of each others observations, grasped the essential 

 features of these very important and characteristic structures of 

 the avian lung. Although they were figured by earlier observers 

 (Campana, '75, Fischer, '05), Schulze was the first to observe 

 carefully their arrangement and relation to the air-sacs and to 

 the other bronchi in a number of different birds, and to appreci- 

 ate their physiological role, while Juillet added some morpho- 

 logical facts and made observations on their development. 



Review of the extensive literature on the air-sacs seems to us 

 unnecessary, since the bulk of it relates to their position, size and 

 anatomical relationships in the adult. In this respect the papers 

 of Campana, '75, Bruno Muller, '07, and Schulze. '11, are espe- 

 cially good. As regards their development, except for the paper 

 of Bertilli, little has been added to the embryology of the air- 

 sacs since Selenka's paper of 1866 in which he described and fig- 

 ured their development in the chick. 



The recurrent bronchi, however, have come into notice more 

 recently and a brief account of the published observations on 

 these structures should be given. 



Campana ('75) in his extensive memoir dealing with the res- 

 piratory apparatus of birds and confined chiefly to a description 

 of the adult structures, described the air-sacs and bronchial tree. 

 He also made a careful analysis of the orifices connecting lung 

 and air-sacs. Examination of his figures shows that some of the 

 recurrent bronchi also stand out quite distinctly, but Campana 

 considered them as the result of a reconstitution into a single 

 trunk of several tertiary bronchi, without recognizing their true 

 nature. He apparently considered them as merely a part of 

 the network of air passages with no special significance attached 

 to them. 



On the other hand Campana used the term 'Bronche recurrente' 

 in an entirely different connection, applying it to the curvilinear 

 branch of the first entobranchus. This statement should be 

 made to prevent confusion. 



Guido Fischer ('05) likewise figures the recurrent bronchi of 

 several of the air-sacs. The only reference he makes to these 



