The quadratojugal is a small jaw bone that is present in most amphibians, reptiles and birds, but has been lost in mammals. It is connected to the jugal as well as other bones, though these may vary with species.
The quadratojugal bone is a small bone between the cheek and otic notch. Squamates (lizards and snakes) lack a quadratojugal bone.
References
Quadratojugal bone Wikipedia(Text) CC BY-SA