GREAT TERN. 
243 
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. 
