The lung of birds is the most complex and efficient gas exchanger in the air‐breathing vertebrates. A total number of 27 normal Japanese quail embryos during the pre‐hatching period were used. The current work aimed to investigate the histomorphological, histochemical and ultrastructural changes of the lung at different stages of development using light and electron microscopy. The results showed that the respiratory primordium was observed on the 2nd embryonic day (ED) as a ventral out‐pouching of the primitive foregut into the surrounding mesenchyme. The first evidence of the lung buds appeared on the 3rd ED. On the 4th ED, the buds increased in size. In addition, the secondary bronchi budded from the epithelial lining of the primary bronchus into the surrounding mesenchyme. On the 6th ED, the number of the secondary bronchi increased and began to give rise small tubules (parabronchi). On the 7th …