2,?2 SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. SO 



large ampulla, but is only slightly developed in the pigeon. In its 

 further course the mesobronchium narrows considerably, and at its 

 posterior end, the ostium posterius, it is not wider than the other 

 air-tubes that approach that opening. In the literature on this 

 subject it is usually stated that the mesobronchium opens into the 

 saccus abdominalis with a wide orifice. Perhaps this may occur nor- 

 mally in other birds ; in the pigeon I have seen such an arrangement 

 only once. 



From the middle of the mesobronchium there is given off ventrally 

 a branch-canal which, on account of its small caliber, is to be con- 

 sidered an accessory passage. Unlike the mesobronchium, it retains 

 throughout its course the same width. It extends to the ostium 

 intermedium posterius (figs. 8, 9, 10, 12, OIP), which is situated on 

 the posterior border of the lung, laterally and a little ventrally from 

 the ostium posterius. Some distance before reaching this opening 

 the canal lies just below the ventral surface of the lung (fig. 8). 



The wall of the mesobronchium is perforated by numerous open- 

 ings which lead into canals supplying the lung and the air-sacs with 

 air. Those supplying the lung itself are the entobronchia ; those 

 extending beyond the lung and supplying the air-sacs, the ecto- 

 bronchia. Besides numerous small openings, eleven large ones can 

 be distinguished. All these lie upon the dorsal side of the meso- 

 bronchium. In the anterior portion of the mesobronchium — that is 

 to say, in the vestibulum — there are four large openings quite close 

 together. From these the entobronchia take their origin. The 

 seven other openings are smaller and situated at nearly equal dis- 

 tances from each other in the remaining central and posterior por- 

 tions of the mesobronchium. Their size decreases posteriorly. These 

 openings lead into the seven ectobronchia (fig. 10, ECT). Sappey 

 calls the entobronchia "bronches divergentes" ; the ectobronchia, be- 

 cause they run near the ribs, "bronches costales." The former 

 are regular, the latter irregular. From the ento- and ectobronchia 

 lateral branches, the parabronchia (Lungenpfeifen; canaux tertiaires, 

 Cuvier; bronchial tubes) are given off. These are so numerous, 

 and the holes in the sides of the ecto- and entobronchia, which 

 lead into them, lie so close together that the walls of these canals 

 have a sieve-like appearance. The angles at which the parabronchia 

 leave the ecto- and entobronchia always closely approach a right 

 angle, but apart from this, these branch canals are variously ar- 

 ranged in one row, in two rows, or spirally. These parabronchia 

 impart to the bird's lung its characteristic appearance. They often 

 anastomose with each other, and I have found that occasionallv the 



