The shaft of the feather, or the quill, is called the calamus at the end where it is attached under the skin, and the rachis where it extends above the skin to the tip of the feather. The sides of the feather are called vanes, and are made up of fibres called barbs, coming off the rachis at an angle. On the barbs are smaller fibres called barblets, with hooklets that hold them together like a zipper.