Exapophyses
Exapophyses are bony joints present in the cervicals of some pterosaurs. Exapophyses lie on the centrum, the spool-shaped main body of each vertebra, where they are positioned adjacent to the main articulating surfaces between centra. Exapophyses which are next to the cotyle are known as preexapophyses while those at the condyle are called postexapophyses. Exapophyses act as accessory articulations, meaning that they complement the cotyle and condyle, as well as the zygapophyses. The term was coined by Samuel Wendell Williston in 1897 during a description of Pteranodon. Exapophyses are a defining trait of the pterosaur subgroup Eupterodactyloidea, although they are also known to occur in some ctenochasmatids. Rhamphorhynchids have paired, knob-like extensions on the condyle which are occasionally also termed exapophyses, but these extensions are not distinctly offset and are not considered homologous to the exapophyses of eupterodactyloids and ctenochasmatids.
