Kenneth, Kardong. Vertebrates: Comparative anatomy, function, evolution. 3rd ed. New York : McGraw-Hill, 2002.

http://www.earthlife.net/birds/anatomy.html

http://merops.sanger.ac.uk/speccards/peptidase/SP000252.htm

http://www.nhm.org/birds/guide/pg003.html

http://www.biology.eku.edu/RITCHISO/skeleton.html

http://www.digimorph.org/specimens/Gallus_gallus/day12/