60 THE STRUCTURE OF THE FOWL 



in a manner comparable to vocal folds of the 

 mammalian larynx. 



The bright-red lungs are closely applied by 

 their dorsal surface to the vertebral column 

 and the ribs. Consequently this face is deeply 

 indented by grooves, each corresponding to a 

 rib (Fig. 12). The ventral surface is free, and 

 covered by pleura and the rudimentary and 

 largely tendinous diaphragm. The narrow 

 cranial end of each organ reaches as far as the 

 first rib ; while the broader caudal end touches 

 the kidney. 



The ventral surface of each lung is pierced 

 by a bronchus, which passes through the whole 

 length of the lung and communicates finally 

 with the abdominal air-sac. The extra-pul- 

 monary part of the bronchus has its wall 

 strengthened by half-rings of cartilage with 

 membrane completing the tube. 



Within the lung the main bronchus, or 

 mesohronchus, gives off ten secondary bronchi — 

 the first four large, the remaining six smaller — 

 which communicate directly or indirectly with 

 air-sacs, and from which tertiary bronchi or 

 parabronchia pass in a radiate or pennate 

 manner towards the surface of the lung where 

 they end blindly. Muscular tissue is present 



