RESPIRATORY ORGANS. 



261 



parabronchi are to be compared to bronchioles, the diverticula to 

 infundibula. 



The mesobronchus and usually four other bronchi do not stop at 

 the lung wall, but are continued as thin walled vesicles, the air sacs, 



sad 



FIG. 272. Air sacs of pigeon, after Bruno Muller. c l , e 3 , intertrans verse canal; 

 da 1 , da 2 , axillary diverticulum and its ventral outgrowth; dc> diverticulum cos tale; dfa, 

 dfp, divert, femorale anterior et posterior; dot, divert, cesophago-tracheale; ds, div. sub- 

 scapulare; dst, div. sternale; PC, preacetabular canal; sad, sas, saccus abdominalis dexter et 

 sinister; sc, saccus cervicalis; sia, sip, saccus intermedius, anterior et posterior. 



structures peculiar to birds (and in a slight extent to chameleons) and 

 occurring in all recent species. Each sac (figs. 271, 272) has received 

 several names. The sub-bronchial, anterior to the furcula, is usually 

 unpaired. The cervical, lateral to the first, lies at the base of the 



