90 



ANATID.E. 



to exhibit tlie various circular aucl oval apertures which per- 

 vade difFereut parts of this bony enlargement, the opposite 

 sides not being exactly alike, either in the number, form, 

 or situation of these apertures in the bone, which in a natural 

 state are closed by delicate transparent membrane. The 

 bronchial tubes are divided higher at the back than in front, 

 as seen in the figure on the left, to allow free passage for 

 the oesophagus between them from behind forwards. 



