GREAT TERN 



79 



opening door, rusted on its hinges. The bone of the skull is re- 

 markably thick and strong, as also the membrane that surrounds 

 the brain; in. this respect resembling the Woodpecker^s. In both 

 this provision is doubtless intended to enable the birds to support, 

 without injury, the violent concussions caused by the plunging of 

 the one, and the chiselling of the other. 



