“Perhaps the most striking feature of the endoskeleton of birds is its pneumaticity.”
“Some interesting exceptions to the correlation between body size and pneumaticity occur in birds that dive underwater to feed, such as grebes, loons, and penguins.”
“Postcranial pneumaticity is absent in all other extant vertebrates with the known exceptions of osteoglossomorph fish and the hyoid bone in howler monkeys.”
pneumatique
(historical) The pneumatic postal system in Paris (abolished 1984), or a letter sent by this system.