The zygosphene-zygantrum articulation is an accessory joint between vertebrae found in several
lepidosauromorph
Lepidosauromorpha (in PhyloCode known as ''Pan-Lepidosauria'') is a group of reptiles comprising all diapsids closer to lizards than to archosaurs (which include crocodiles and birds). The only living sub-group is the Lepidosauria, which contains ...
reptiles. This
pivot joint
In animal anatomy, a pivot joint (trochoid joint, rotary joint or lateral ginglymus) is a type of synovial joint whose movement axis is parallel to the long axis of the proximal bone, which typically has a convex articular surface.
According to o ...
consists of a forward-facing, wedge-shaped
process
A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic.
Things called a process include:
Business and management
*Business process, activities that produce a specific se ...
called the zygosphene, that fits in a depression on the rearside of the next vertebrae, called the zygantrum.
The zygosphene sits between the
prezygapophysis
The articular processes or zygapophyses (Greek ζυγον = "yoke" (because it links two vertebrae) + απο = "away" + φυσις = "process") of a vertebra are projections of the vertebra that serve the purpose of fitting with an adjacent vertebr ...
in the
neural arch, whereas the zygantrum sits between the
postzygapophysis
The articular processes or zygapophyses (Greek ζυγον = "yoke" (because it links two vertebrae) + απο = "away" + φυσις = "process") of a vertebra are projections of the vertebra that serve the purpose of fitting with an adjacent vertebr ...
.
This joint is found in
snakes
Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joi ...
,
lacertids,
teiids,
Gymnophthalmids as well as in some
iguanids and
cordylids.
It is also found in several fossil groups such as
plesiosaurians,
nothosauria
Nothosaurs (order Nothosauroidea) were Triassic marine sauropterygian reptiles that may have lived like seals of today, catching food in water but coming ashore on rocks and beaches. They averaged about in length, with a long body and tail.F. v. ...
ns and
pachypleurosaurians.
It is absent in today's
Monitor lizard
Monitor lizards are lizards in the genus ''Varanus,'' the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species. About 80 species are recogn ...
(''Varanus''), but occurs in fossil Varanids.
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.
See also
*
Hyposphene-hypantrum articulation The hyposphene-hypantrum articulation is an accessory joint found in the vertebrae of several fossil reptiles of the group Archosauromorpha. It consists of a process on the backside of the vertebrae, the hyposphene, that fits in a depression in the ...
, in the
Archosauromorpha
Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, liza ...
References
[{{cite book , last=Romer , first=Alfred Sherwood , title=Osteology of the Reptiles , publisher=The University of Chicago Press , isbn=0-226-72487-5 , year=1956 , page=256]
Reptile anatomy