ANATO:\rY OF THE FOWL 31 



sac). It terminates close to the middle of the lung, where it 

 communicates, through a snuiU opening, witli tlie diaphrag- 

 matic air sac. 



The bronchus cervicalis extends forward in the direction oP 

 the original trunk and anteriorly ccmimunicates with the cer- 

 vical air sac through the ostium cervicale. 



There is also given off from the main bronchus the bronchus 

 cervicularis dorsalis and medialis. The first extends witli a 

 few bronchi into the clavicular air sac. The bronchus dia- 

 phragrnaticus cranialis extends laterally, dorsally and medi- 

 ally, and terminates in the thoracic air sac through the ostium 

 intermedium craniate. The bronchus caudalis originates 

 from the dorso-median wall and extends to the caudal and 

 middle portions of the lung. There is given off another 

 bronchus called the bronchus lateralis from this lateral bron- 

 chus. 



There extend from the main bronchus several bronchi in 

 the medial half of the lung. There are six to ten dorsal 

 bronchi (bronchi dorsales). Numerous perpendicular, nar- 

 row, thick-walled tubes lying close to each other are given off 

 from the dorsal Avail of the main l)ronchus and other bronchi 

 mentioned. These tubes have been called the ^'lung pipes," 

 which by lateral pressure become five- or six-sided tubes. The 

 mass of the lungs are made up of these tubes. These tubes 

 terminate near the surface of the lung. The ends of these 

 tulies, Avhicli lie at right angles to the main channel, form 

 sacculations somewhat simulating the air sacs of mammals. 

 Connective tissue, through which pass l)lood vessels and nerves, 

 fills in the space between these lung tubules. 



Air Sacs 



The air sacs are bladderlike structures with delicate walls. 

 The sacs are lined with a mucous membrane which is a con- 

 tinuation of the mucous membrane of the bronchi. They are 

 connected with the bronchial tubes but do not communicate 

 with each other. They also communicate with air spaces in 

 m'-^.ny of the bones of the trunk and limbs. Bronchial tubes 

 extending to the surface of the lung communicate directly 

 Avith these air cells. The air sacs continue partly into the 

 bones and line the Avails of these spaces. These air spaces, 

 some of Avhich are of considerable size, add to the bulk of the 

 body of the bird Avitliout increasing its Aveight. They reach 

 their highest state of development in the fliers and SAvimmers 

 and are less developed in running birds. The air sacs are as 

 folloAvs : The anterior thoracic air sac, from Avhich arises the 



