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, 
Fic. 272.—Air sacs of pigeon, after Bruno Muller. c, c*, intertransverse canal; 
da‘, da”, axillary diverticulum and its ventral outgrowth; dc, diverticulum costale; 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 
