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 (Lecointre 380). Squamates (lizards and snakes) lack a quadratojugal bone (Schwenk 193).
Lecointre G, Le Guyader H. The tree of life: a phylogenetic classification. Belin-Paris: The President and Fellows of Harvard College; 2006. 563 p. Available from: http://books.google.com/books?id=S4LxB9MRdzMC&lpg=PA38.... Accessed 2011 Dec. 10.
Schwenk K. Feeding: Form, Function and Evolution in Tetrapod Vertebrates. San Diego (Ca): Academic Press; 2000. 537 p. Available from: http://books.google.com/books?id=f7exUolnxugC&pg=PA193.... Accessed 2011 Dec. 10.
