Zygomatic plate

In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch (cheekbone). At the back, it connects to the front (maxillary) root of the zygomatic arch, and at the top it is connected to the rest of the skull via the antorbital bridge. It is part of the maxillary bone, or upper jaw, which also contains the upper cheekteeth. Primitively, rodents have a nearly horizontal zygomatic plate. In association with specializations in zygomasseteric system, several distinct morphologies have developed across the order.

The term is also used for an analogous structure in some South American typotheres, including Pseudotypotherium and Medistylus.

The zygomatic plate serves to resist muscular tension resulting from the contraction of the incisors by the anterior deep masseter muscle; thus, rodents which pulverize hard food with the incisors tend to have broader zygomatic plates than those that rather use their molars for this purpose.

The members of this large and diverse suborder have a narrow, low zygomatic plate.

The suborder Sciuromorpha includes three families.Squirrels (family Sciuridae) tend to have broad zygomatic plate that extend above the infraorbital foramen. The mountain beaver (Aplodontia rufa), the only surviving member of its family, retains the primitive narrow and low plate. The dormice (Gliridae) have broad, high zygomatic plates, except for Graphiurus, which has a lower plate.

Members of the suborder Castorimorpha, which includes the beavers, pocket gophers, and pocket mice, tend to have broad zygomatic plate that extend above the infraorbital foramen.

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