148 



Diseases of Poultry 



posterior end of its lung where it opens into the abdominal 

 air sac. This relation is shown in Fig. 26. 



The primary bronchus gives off secondary bronchi which 

 radiate toward the surface of the lungs. The secondary 

 bronchi give off smaller radiating branches, the tertiary 

 bronchi. Both primary and secondary bronchi remain of 



practically uniform 

 diameter through- 

 out their entire 

 length. For the 

 most part these 

 tubes end blindly, 

 but some of them 

 communicate with 

 the air sacs. This 

 tubular system 

 makes up the air- 

 containing portion 

 of the lungs. It is 

 embedded in a net- 

 work of almost 

 naked blood vessels 

 which make up the 

 spongy tissue of the 

 lungs. The aera- 

 tion of the blood 

 takes place through 

 the walls of these vessels. The intimate relations of the 

 tubular and vascular sj'stems of the lungs are shown in 

 Fig. 28. 



The air sacs are \'ery large, thin-walled sacs which open 

 into the bronchial tubes as described. When expanded 

 with air these sacs fill all the available space in the thoracic- 

 abdominal cavity and axilla. A small sac also lies along the 



Fig. 26. — Diagrammatic drawing of the left 

 lung of a domestic fowl, a, primary bronchus ; 

 ft, secondary bronchus ; V, openings of other 

 secondary bronchi ; c, opening of tertiary 

 bronchus ; d, openings into air sacs. (Origi- 

 nal.) 



