uncinate processes of ribs
The uncinate processes of the ribs are extensions of bone that project caudally from the vertical segment of each rib. (Uncinate means hooked from Latin uncinatus, from uncinus, barb, from uncus, hook.) They are found in birds (except for screamers), reptiles, and the early amphibian Ichthyostega.{{cite book|last=Kardong|first=Kenneth V.|title=Vertebrates: comparative anatomy, function, evolution|year=1995|publisher=McGraw-Hill|isbn=0-697-21991-7|pages=55, 57}}
These processes can serve to attach scapula muscles, and help to strengthen the rib cage overlapping with the rib behind them.{{Cite book| last1 = Bonney| first1 = Rick | last2 = Rohrbaugh, Jr.| first2 = Ronald| title = Handbook of Bird Biology| place= Princeton, NJ| publisher = Princeton University Press| year = 2004| edition = Second| isbn = 0-938027-62-X}} They are also shown to have a role in respiration by increasing the effectiveness of muscles involved in inspiration including the appendicocostal muscles.Codd, J. R., D. F. Boggs, S. F. Perry, and D. R. Carrier. 2005. Activity of three muscles associated with the uncinate processes of the giant Canada Goose Branta canadensis maximus. Journal of Experimental Biology 208:849-857. [http://jeb.biologists.org/cgi/content/full/jexbio;208/5/849 Full text] The processes are short in walking birds and long in diving species and are of intermediate length in non-specialist birds.Tickle, Peter G., A. Roland Ennos, Laura E. Lennox, Steven F. Perry and Jonathan R. Codd 2007. Functional significance of the uncinate processes in birds. Journal of Experimental Biology 210:3955-3961 [http://jeb.biologists.org/cgi/content/abstract/210/22/3955 Abstract] The screamers (Anhimidae) are unique in lacking this process.{{cite book|title=Biology, medicine, and surgery of South American wild animals|author=Fowler ME & Cubas ZS |year=2001|publisher=Wiley-Blackwell|page=103}} The process has also been noted in some enantiornitheans.Fucheng, Zhang, Zhou Zhoghe, Hou Lianhai & Gu Gang 2001. Early diversification of birds: Evidence from a new opposite bird. Chinese Science Bulletin. 46(11):945-949 [http://www.ivpp.ac.cn/pdf/magazine193.pdf PDF]{{Dead link|date=July 2018 |bot=InternetArchiveBot |fix-attempted=no }} Although among living vertebrates, bony uncinate processes are unique to birds, cartilaginous uncinate processes are present in crocodiles. The uncinate process has also been reported in Sphenodon and fossil vertebrates including Caudipteryx, oviraptorids, dromaeosaurids,{{Cite journal|last1=Codd|first1=Jonathan R|last2=Manning|first2=Phillip L|last3=Norell|first3=Mark A|last4=Perry|first4=Steven F|date=2008-01-22|title=Avian-like breathing mechanics in maniraptoran dinosaurs|journal=Proceedings of the Royal Society B: Biological Sciences|volume=275|issue=1631|pages=157–161|doi=10.1098/rspb.2007.1233|issn=0962-8452|pmc=2596187|pmid=17986432}}{{Cite book|last=Paul|first=Gregory S.|url=https://www.worldcat.org/oclc/18350868|title=Predatory dinosaurs of the world : a complete illustrated guide|date=1988|isbn=0-671-61946-2|location=New York|oclc=18350868}} Confuciusornis, Chaoyangia, and Longipteryx; however it apparently does not occur in Archaeopteryx, though Codd et al. (2007) reported uncinate processes in Archaeopteryx.