thumb|Diagram showing homologous bones of the skulls of a [[monitor lizard and a crocodile. Jugal bone labelled Ju, in pale green, at centre left.]]
The jugal is a skull bone found in most jawed vertebrates. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species.
Taxonomic distribution
thumb|Skulls of the early jawed vertebrates [[Entelognathus, Qilinyu, and Bianchengichthys, with the jugal highlighted in green]]
The jugal is present in placoderms as the suborbital plate. The jugal and lacrimal bones are the only two remaining from the ancestral circumorbital series: the prefrontal, postfrontal, postorbital, jugal, and lacrimal bones.
In dinosaurs
This bone is considered key in the determination of general traits in cases in which the entire skull has not been found intact (for instance, as with dinosaurs in paleontology). In some dinosaur genera the jugal also forms part of the lower margin of either the antorbital fenestra or the infratemporal fenestra, or both. Most commonly, this bone articulates with the quadratojugal, the postorbital, the lacrimal, and the maxilla. In horned dinosaurs, like Pentaceratops, the jugal bone is thick and comes to a point, which has led paleontologists to refer to it as the "jugal horn".
Development
During development, the jugal bone originates from dermal bone. In at least some mammals, it forms from two ossification centers, which sometimes can remain separate into adulthood.
In birds
While the jugal bone is thick and straplike in most other reptiles, the jugal bone is thin and strutlike in birds. This is thought to reduce the weight of the skull and facilitate cranial kinesis.
In mammals
thumb|Skull of stem-mammal [[Morganucodon, with jugal labelled]]
In mammals, including humans, the jugal bone is more commonly referred to as the zygoma. It assists in constructing the facial contour, protecting the eye from damage, and providing attachment sites for facial muscles. The zygoma provides important functions as the origin of the masseter muscle and as a point of resistance for masticatory forces. Preliminary studies also indicate that variation in zygomatic structure may be useful in determining ancestral origins of modern human populations.
References
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