1 82 NATURAL HISTORY ESSAYS 



tion of respiration. Thus the whale is safeguarded 

 against being drowned, and can with impunity open 

 his mouth to feed below the surface, just as a crocodile 

 or alligator can. In the common porpoise the velum 

 palati forms a true curtain hanging well down the 

 back of the mouth, while the trachea plays through a 

 hole in the palate surrounded by a compressor 

 muscle. The spiracular valve of the porpoise has 

 been happily described by Frank Buckland as "a 

 combination of the conical stopper of a wine decanter 

 with the action of the bolts of a door lock." 



