Zygomatic plate

[5] 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.

[8] Squirrels (family Sciuridae) tend to have broad zygomatic plate that extend above the infraorbital foramen.

[9] The mountain beaver (Aplodontia rufa), the only surviving member of its family, retains the primitive narrow and low plate.

[14] Members of the subfamily Idiurinae are atypical in having the zygomatic plate extended forward nearly to the incisors.

[8] In the most numerous subgroup, the Muroidea (including all living families except Dipodidae), the zygomatic plate is generally broad and tilted upwards.

[18] Members of the family Dipodidae, which have hystricomorphous zygomasseteric morphology, have nearly horizontal, narrow zygomatic plates.

[21] The mouse-like hamster (Calomyscus), the only member of its family, has a straight front margin on the zygomatic plate.

Except for Xeromys, Hydromys and related genera ("hydromyines") have a narrow plate, lacking the notch, as does Hyomys,[32] Macruromys, Crunomys,[31] and Rhynchomys.

[33] The Philippine Batomys, Carpomys, and Crateromys have well-developed zygomatic plates, reminiscent of those in Arvicolinae.

[37] Members of the subfamily Sigmodontinae, which includes a number of tribes, usually have the antorbital bridge below the upper surface of the skull.

[42] Most members of the tribe Phyllotini have the antorbital bridge located higher than is usual in Sigmodontinae (Calomys and Andalgalomys show the normal sigmodontine condition).

In contrast, Microryzomys, Oreoryzomys, Oecomys, Scolomys, and Sigmodontomys aphrastus lack a well-defined notch and do not have the plate extending appreciably in front of the root of the zygomatic arch.

[53] The zygomatic plate extending back to the level of the upper first molar is a putative synapomorphy of Clade C within Oryzomyini.