The rostrum (front part of the skull) is short. The broad zygomatic plate develops a prominent notch, but not a spine, on its front end, and its back margin is in front of the first molars. The interorbital region, located between the eyes, is narrowest towards the front and is flanked by beadings along its margins. The interparietal bone is relatively long. The incisive foramina, perforations of the palate between the incisors and the molars, are narrow and long and taper towards the end. The palate itself is also long, extending beyond the molars, and includes prominent posterolateral palatal pits near the third molars, which are excavated into deep . The roof of the mesopterygoid fossa, the opening behind the palate, is not perforated by sphenopalatine vacuities. "O. gorgasi" lacks an alisphenoid strut; in some other oryzomyines, this extension of the alisphenoid bone separates two openings in the skull, the masticatory–buccinator foramen and the foramen ovale accessorium. The squamosal bone lacks a suspensory process that contacts the tegmen tympani, the roof of the tympanic cavity, a defining character of oryzomyines. The subsquamosal fenestra, an opening at the back of the skull determined by the shape of the squamosal, is almost absent.