Uncinate processes of ribs

The uncinate processes of the ribs are extensions of bone that in birds project caudally from the vertical segment of each rib. (Uncinate means "hooked" from Latin "uncinatus", from "uncinus", barb, from "uncus", hook.) These processes help to strengthen the rib cage of birds by overlapping with the rib behind them. [Citation| last = Podulka| first = Sandy | last2 = Rohrbaugh, Jr.| first2 = Ronald| last = Bonney| first = Rick| title = Handbook of Bird Biology| place= Princeton, NJ| publisher = Princeton University Press| year = 2004| edition = Second| isbn = 0-938-02762-X] They are also shown to have a role in respiration by increasing the effectiveness of muscles involved in inspiration including the external intercostal 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 process has also been noted in some Enantiornithines.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] ] Although bony uncinate processes are unique to birds, cartilaginous uncinate processes are present in crocodiles. The uncinate process has also been reported in "Sphenodon", "Caudipteryx", oviraptorids, "Confuciusornis" and "Chaoyangia" however it does not occur in "Archaeopteryx".

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