Editing Bird (section)

===Skeletal system===
{{Main|Bird_anatomy#Skeletal_system}}

The skeleton consists of very lightweight bones. They have large air-filled cavities (called pneumatic cavities) which connect with the [[respiratory system]].<ref>{{cite web|last=Ehrlich |first=Paul R. |author2=David S. Dobkin |author3=Darryl Wheye |title=Adaptations for Flight |url=http://www.stanford.edu/group/stanfordbirds/text/essays/Adaptations.html |year=1988 |work=Birds of Stanford |publisher=[[Stanford University]] |access-date=13 December 2007}} Based on The Birder's Handbook ([[Paul Ehrlich]], David Dobkin, and Darryl Wheye. 1988. Simon and Schuster, New York.)</ref> The skull bones in adults are fused and do not show [[cranial sutures]].<ref name="Gill">{{Cite book |last=Gill |first=Frank |year=1995 |title=Ornithology |publisher=WH Freeman and Co |location=New York |isbn=0-7167-2415-4 }}</ref> The [[orbit (anatomy)|orbital cavities]] that house the eyeballs are large and separated from each other by a bony [[septum]] (partition). The [[vertebral column|spine]] has cervical, thoracic, lumbar and caudal regions with the number of cervical (neck) vertebrae highly variable and especially flexible, but movement is reduced in the anterior [[thoracic vertebrae]] and absent in the later vertebrae.<ref>{{Cite news|title=The Avian Skeleton |url=http://www.paulnoll.com/Oregon/Birds/Avian-Skeleton.html |work=paulnoll.com | last=Noll | first=Paul |access-date=13 December 2007}}</ref> The last few are fused with the [[pelvis]] to form the [[synsacrum]].<ref name="Gill"/> The ribs are flattened and the [[sternum]] is keeled for the attachment of flight muscles except in the flightless bird orders. The forelimbs are modified into wings.<ref>{{Cite news|title=Skeleton of a typical bird |url=http://fsc.fernbank.edu/Birding/skeleton.htm |work=Fernbank Science Center's Ornithology Web |access-date=13 December 2007}}</ref> The wings are more or less developed depending on the species; the only known groups that lost their wings are the [[extinct]] [[moa]] and [[elephant bird]]s.<ref>{{Cite web |url=https://www.nationalgeographic.com/science/phenomena/2014/05/22/the-surprising-closest-relative-of-the-huge-elephant-birds/|archive-url=https://web.archive.org/web/20181214065448/https://www.nationalgeographic.com/science/phenomena/2014/05/22/the-surprising-closest-relative-of-the-huge-elephant-birds/|url-status=dead|archive-date=14 December 2018|title=The Surprising Closest Relative of the Huge Elephant Birds|date=22 May 2014|website=Science & Innovation|access-date=6 March 2019}}</ref>