Most birds have a raised central keel on their breastbone, to which their main flight muscles are attached. But ratites have a flat breastbone. This etching, which appeared in Richard Owen’s Memoirs on the extinct wingless birds of New Zealand in 1879, illustrates the absence of a keel in kiwi.
Te whakamahi i tēnei tūemi
National Library of New Zealand, General Lending Collection
Reference: Richard Owen, Memoirs on the extinct wingless birds of New Zealand. London: John Van Voorst, 1879, plate VIII
Permission of the National Library of New Zealand, Te Puna Mātauranga o Aotearoa, must be obtained before any re-use of this image.