Zygosphene-zygantrum articulation

The zygosphene-zygantrum articulation is an accessory joint between vertebrae found in several lepidosauromorph reptiles. This pivot joint consists of a forward-facing, wedge-shaped process called the zygosphene, that fits in a depression on the rearside of the next vertebrae, called the zygantrum.^[1] The zygosphene sits between the prezygapophysis in the neural arch, whereas the zygantrum sits between the postzygapophysis.^[2]

This joint is found in snakes, lacertids, teiids, Gymnophthalmids as well as in some iguanids and cordylids.^[3] It is also found in several fossil groups such as plesiosaurians, nothosaurians and pachypleurosaurians.^[4] It is absent in today's Monitor lizard (Varanus), but occurs in fossil Varanids.^[5]

The zygosphene-zygantrum joint's function is to stabilize the vertebral column. While it permits horizontal and vertical movements of the vertebral column, it prevents rotations of the single vertebrae against each other.^[5]

See also

• Hyposphene-hypantrum articulation, in the Archosauromorpha

References

1. Rieger, Gunde; Westheide, Wilfried (2009-10-29). Spezielle Zoologie. Teil 2: Wirbel- oder Schädeltiere (in German). Springer DE. p. 381. ISBN 9783827420398.
2. Callaway, Jack M.; Nicholls, Elizabeth L. (1997-03-12). Ancient Marine Reptiles. Academic Press. p. 125. ISBN 9780080527215.
3. Estes, Richard; de Queiroz, Kevin; Gauthier, Jacques (1988). "Phylogenetic Relationships within Squamata". In Richard J. Estes (ed.). Phylogenetic Relationships of the Lizard Families: Essays Commemorating Charles L. Camp. Stanford University Press. p. 166. ISBN 9780804714358.
4. Benton, Michael J. (2005). Vertebrate palaeontology (3. ed.). Blackwell Science. p. 150. ISBN 0-632-05637-1.
5. Romer, Alfred Sherwood (1956). Osteology of the Reptiles. The University of Chicago Press. p. 256. ISBN 0-226-72487-5.