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. The zygosphene sits between the prezygapophysis in the neural arch, whereas the zygantrum sits between the postzygapophysis.