294 



COMPARATIVE ANATOMY 

 .--m.l.c 



FIG. 238. LEFT LUNG or THE DUCK, in situ. (From a drawing by H. Strasser. 

 The main bronchus is cut open ; internally to it lies the pulmonary vein, and 

 externally the pulmonary artery. 



Oe, oesophagus; m.l.c, muse, longus colli ; Br. Ws, thoracic vertebrae ; v, v, ends 

 of free vertebral ribs ; #tv, stv, sections of ribs which are connected with the 

 sternum ; N, kidney ; Tr, trachea, /, first entobronchium, and c, its ostium 

 communicating with the prebronchial air-sac ; i, a, e, its internal, anterior, 

 and external branches ; Ili, lie, internal and external branch of the second 

 entobronchium : the end of lie opens into the sub-bronchial sac at d ; ///, 

 third entobronchium, with the aperture for the anterior intermediate air- sac ; 

 IV, fourth entobronchium ; au, opening of the main bronchus into the 

 abdominal sac ; b, opening of the outer lateral branch of the mesobronchium 

 into the posterior intermediate air-sac ; ft 1 , second ostium of the latter, more 

 towards the middle line (present in Passeres). The boundary of the pul- 

 monary aponeurosis is seen along the outer edge of the lung, and the costo- 

 pulmonary muscles are shown extending from it to the ribs. 



anteriorly to the hilum of the lung, and gives off internal, external and 

 anterior branches, one of which opens into the prebronchial sac. The other 

 entobronchia give rise to two series of branches, one of which extends 

 inwards and backwards between the factors of the pulmonary vein, and the 

 other outwards between the arterial branches. Almost without exception 

 a large aperture or ostium is present on the wall on the third entobronchium, 



