172 MILLER. [Vol. VIII. 



siderably from that of the reptile or from that of the mammal. 

 This difference seems to be so great that in the past it has 

 been very difficult to compare them satisfactorily. As soon as 

 the bronchus enters the lung it breaks up into a number of 

 tubes, one of which is shown in Fig. 9. Each of these tubes 

 rapidly breaks up into a number of pipes which lie in great part 

 immediately below the surface of the lung and clasp it as tongs 

 from all sides. These tubes are not real bronchi, because 

 their structure is very different and because they do not end 

 as do the terminal bronchi of mammals. In comparative 

 anatomy they are known as canaliculi aeriferi, or air pipes. 

 The pipes just below the surface of the lung anastomose 

 freely, as shown in Fig. 9, and also send blind tubes into the 

 interior of the lung, which meet but do not communicate with 

 those from the opposite side. At points where two or more 

 of the pipes unite there are large openings which communicate 

 with the air-sacs or bags of the abdominal cavity, bones, etc. 

 In order to avoid confusion, I shall speak of them as air-bags 

 to differentiate them from the air-sacs of other lungs. The 

 bags must be considered as an integral portion of the lung, 

 for they are continuous with the air-pipes and are also de- 

 veloped directly from them.^ 



From each air-pipe, all along its course, the alveoli, or true 

 lung structure, arise. ^ Now how shall this be brought into 

 connection with the reptilian lung } It is very simple. The 

 air-pipes are nothing more than the atria of the crocodile's 

 lung, only that in the bird they are more turned upon one 

 another and anastomose. From the air-pipes or atria, as I 

 shall now call them, the air-sacs or proper lung substance 

 arise. The whole is clear when cuts 5 and 6 are compared. 



In the bird we have the important intermediate links between 

 the reptile and the mammal (compare cuts 4, 5, 6, and 7). 

 It is the first beginning of a branching bronchus. Up to the 

 present we have had only a single terminal bronchus or a 

 bronchus perforated along its sides. Up to the present we 



1 Weldon, Proceedings of the Zool. Society, 1883. Butler, ibid, 1889. Mall, 

 Journal of Morphology, Vol. 5. 



2 F. E. Schultze, Strieker's Handbuch, 1871. 



