In Other Animals
In non-mammalian vertebrates, the zygomatic bone is referred to as the jugal bone, since these animals have no zygomatic arch. In coelacanths and early tetrapods the bone is relatively large. Here, it is a plate-like bone forming the lower margin of the orbit and much of the side of the face. In ray-finned fishes it is reduced or absent, and the entire cheek region is generally small. The bone is also absent in living amphibians.
With the exception of turtles, the jugal bone in reptiles forms a relatively narrow bar separating the orbit from the inferior temporal fenestra, of which it may also form the lower boundary. The bone is similarly reduced in birds. In mammals, it takes on broadly the form seen in humans, with the bar between the orbit and fenestra vanishing entirely, and only the lower boundary of the fenestra remaining, as the zygomatic arch.
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