242 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



Verteb rates the upper, part of the trachea may be con- 

 verted into a vocal organ. 



In the skulls of certain Vertebrates, such as the 

 crocodile and the whale, certain modifications of the 



bones of the palate 

 bring about an elon- 

 gation of the nasal 

 passages and an ap- 

 proximation of the 

 posterior nares to 

 the opening of the 

 trachea (see page 

 344) ; by 

 these means 

 water is pre- 

 vented, at 

 least in part, 

 from passing 

 into the 

 lungs. Other adaptive 

 modifications to the 

 same purpose may be 

 conveniently consi- 

 dered here. 



In the Whales the 

 glottis, or opening 

 into the trachea, is 

 produced into a fun- 

 nel - like projection, 

 which extends into 

 the soft palate, and is 



embraced by its sides. By this means the trachea is 

 brought into direct connection with the nasal passages, 

 the air does not enter at all into the cavity of the 

 mouth, and the water flows on either side into the 

 gullet. A similar disposition of the glottis obtains 

 in the young of the Marsupials, which, born at an 



B 



Fig. 102 A. Bronchial Tree of a Bird. 



p, Pulmonary artery ; A, eparterial ; B, hypar- 

 terial broncbial systems ; v, ventral ; d, 

 dorsal branches. 



