GREAT TERN. 343 



hinges. The bone of the skull is remarkably thick and strong, 

 as also the membrane that surrounds the brain; in this respect 

 resembling the Woodpecker's. In both, this provision is doubt- 

 less intended to enable the birds to support, without injury, the 

 violent concussions caused by the plunging of the one, and the 

 chiseling of the other. 



