The ethmoid frequently appears on the dorsal surface between the frontals.
Prefrontal bones are absent; post-frontals are possibly indicated by a frequently occurring separate centre of ossification in the postorbital process, to which the frontals always contribute.
Many birds possess a more or less well developed cross-joint in front of the frontals and lacrymals, perhaps best developed in Anseres and Psittaci.
The premaxilla is always unpaired, but each half has three long processes directed backwards; one fuses with the maxillary bone, another helps to form the anterior part of the palate, while the third, together with its fellow, forms the " culmen " and extends backwards to the frontals, or rather to the ethmoid which there crops up on the surface.
When one is present it is situated over the conjoined nasal bones; when two, the hinder one is over the frontals.