AVES BIRDS. 631 



(707.) The subsequent changes that occur in the circulatory 

 system of a Bird, namely, the obliteration of the foramen ovale, 

 and of the ductus arteriosi, whereby the pulmonary and systemic 

 circulations become quite distinct, are similar to those which take 

 place in the Mammiferous fetus, and will be described in the next 

 chapter. 



