THE PIGEON. 



245 



the inner face of each bronchus is flat and membranous, and 

 constitutes the membrana tympaniformis interna. 



Ir'" 



Fig. 57. — Columba livia. The lungs filled from the trachea with 

 a solid injection and viewed from the ventral aspect (nat. size). 



In the left lung the bronchus {br, ir') is traced to its termination by 

 dissecting away the overlying substance of the lung. 



hr, principal bronchus : br', br", br"', secondary bronchi : f.a, 

 pulmonary artery : p.v, pulmonary vein : sy, syrinx : tr, trachea : sf.b, 

 aperture for prebronchial air-sac: sb.b, for sub-bronchial: a. in, for 

 anterior-intermediate : p. in, for posterior-intermediate : /, for posterior 

 (ablominal). 



284. The modification of the tracheal rings in the syrinx : the two 

 posterior rings are more widely separated from each other than the rest, 

 and their bony ventral portions send median processes towards one 

 another, which are only separated by a small cartilaginous interval : on 

 the dorsal side these rings are incomplete, but are united with one 

 another on each side of the middle line by a longitudinal cartilaginous 

 bar : the bony first pair of bronchial half-rings are in contact with one 

 another dorsally and ventrally, and, with the distal tracheal rings just 

 described, inclose a chamber, the tympanum. 



285. If the air-sacs, and consequently the lungs, are injected, the 

 secondary bronchi (br', br", br"') will be seen branching out over the 

 anterior and internal regions of the ventral surface of the lungs : they 



