LUNGS 



281 



bronchi. The result of this is that there is no 'bronchial tree' like 

 that of mammals, but a series of anastomosing tubules forming circuits 

 within the lungs. No tubes end blindly. Each parabronchus bears 

 numbers of elongate diverticula, radially arranged, with a narrower 



Fig. 307. — Air sacs and canals of pigeon, after Bruno Mliller. c*"', intertransverse 

 canals; rfa'"*, axillary sac and its ventral diverticulum; dc, canal for ribs; dot, infra- 

 clavicular canal; ds, subscapular sac; dst, sternal canal; pc, preacetabular canal; sad, 

 sas, right and left abdominal sacs; sc, cervical sac; sia, sip, anterior and posterior 

 intermediate sacs. 



basal portion and a larger, lobulatcd, and frequently branched 

 distal part (fig. 305). Apparently the parabronchi are to be com- 

 pared with the bronchioles, the diverticula with the infundibula of 

 other vertebrates. 



Another feature in the birds is the presence of air sacs. The 



