lifewithdeadbirds:

On many of our skulls, you might notice there are small rings of bone in the eye sockets. These are sclerotic rings, and they’re found in many species of bird. It’s thought that these rings, which are also found in many species of reptiles, amphibians, and fish, can help stabilize an animal’s eyeballs. They may also help to keep particularly large eyeballs from straining themselves while the animal is trying to focus its sight on something.

Photo credit: Mary Margaret Ferraro