Zygomasseteric system

The anteroposterior or propalinal (front-to-back) motion of the rodent jaw is enabled by an extension of the zygomatic arch and the division of the masseter into a superficial, lateral and medial muscle.

Several lineages survive into the Oligocene or early Miocene, with only one species still alive today, the mountain beaver (Aplodontia rufa).

The superficial masseter originates on the lateral surface of the anterior maxilla and inserts along the ventral margin of the angular process of the mandible.

[3] suggest that the infraorbital foramen of the extinct sciurid subfamily Cedromurinae may have allowed for the passage of the masseter muscle.

[4] This type gives the greatest anteroposterior component of any rodent zygomasseteric system, which might explain the success of the cosmopolitan Muroidea.