30 POL'LTKY DISEASES 



developed muscle which in fowls, ducks and geese is rudi- 

 nlentar3^ In the male duck the inferior extremity is en- 

 larged into a large sac, called the l)ulla tympaniformi.s. The 

 left bronchus has a perceptible share in the formation of 

 this bulla. This bulla is a resonance box. 



Trachea 



The trachea consists of closed rings round in shape and 

 connected by short connecting bands. In fowls these rings are 

 cartilaginous, while in singing birds they may be partly bony. 

 The trachea is moved by means of two muscles. 



Lungs 



The lungs are two in number, red to pink in color and 

 firmlv connected with the costal wall. The ribs indent the 

 lungs, allowing a part of the outer surface to project slightly 

 })etween them. The ventral free surface is turned towards 

 the body cavity and is covered by the rudimentary diaphragm. 

 The rudimentary diaphragm contains some muscular struc- 

 ture and is attached to the ribs and vertebrae. The pointed 

 anterior lobe extends to the first rib. The posterior part 

 terminates in a broad surface and extends back as far as the 

 anterior end of the kidneys. The bronchi communicate with 

 the air sacs by openings from the posterior border. The two 

 bronchi are broadened after they enter the lung, which is at 

 the beginning of the second third and on the ventral sur- 

 face. They lose their cartilaginous rings and continue as 

 duct-like channels to the extreme posterior edge, where they 

 terminate into cartilaginous rings called the ostium caudale, 

 from which point they communicate with the ventral or large 

 abdominal air sacs. Each bronchus gives off a ventral 

 bronchus, called the bronchus diaphragmaticus caudalis, 

 through which the air is conducted to the ostium intermedium 

 caudale and into the caudal cella thoracica diaphragmatica. 

 Each bronchus gives off lateral bronchi '\\hich extend to the 

 ventral surface of the lung. They form blind pouches or air 

 sacs (alveoli) near the surface of the lung. 



Two bronchial systems take their origin from the main 

 bronchus, the ventral and the dorsal. The bronchus clavicu- 

 laris arises from the dorso-medial wall of the main lironchus 

 a short distance after it enters the lung and ])efore it broad- 

 ens out. This bronchus gives off a large branch, called the 

 bronchus cervicalis. It bends round the base of the main 

 bronchus and the pulmonary artery and supplies the dorsal 

 surface of the lung, and through the ostium claviculare it 

 supplies air to the air sacs on the respective side (dorsal air 



