It shows the characteristic hippopotamus-flange to the lower jaw, but has also a large descending process from the jugal bone of the zygomatic arch of the skull.
The zygomatic arch is variously developed, and the position of the jugal is a character for grouping the families.
The front root of the zygomatic arch is nearly vertical, and placed so far back that it is above the second molar, while the orbit - a unique feature among rodents - is almost completely surrounded by bone.
In the skull the zygomatic arch is slender and the jugal bone small and not extending far forwards, being supported by the long zygomatic process of the maxilla, while the infra-orbital foramen is mostly large, and there are no post-orbital processes.
In the skull the tympanic bulla is hollow, the pterygoid fossa shallow and the zygomatic arch slender, with a rudimentary jugal bone.
Finally, the Philippine Rhynchornys is represented by a rat with two pairs of molars and a long shrew-like nose, the zygomatic arch of the skull being also placed unusually far backward.
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