In the anterodorsal angle of the rim of the orbit the lacrimal bone rests against the frontal and maxillary bones, where the body of the lacrimal contributes to the formation of the posteromedial wall of the nasolacrimal canal. Only a slight part of the maxillary process of the lacrimal remains on each side. The premaxillary bone, which constitutes most of the anterior part of the rostrum, is typically heteromyid in shape. The frontal process is long and slender. On the side of the rostrum the premaxillary forms the anterointernal border of the infraorbital foramen. The ventrolateral border of the bone is expanded slightly and aids in the formation of the tuberosity made by the maxillary bone at the ventroposterior border of the foramen. Ventrally the premaxillary makes up the anterior two-thirds of the lateral wall of the incisive (anterior palatine) foramen. It is not possible to establish what part of the median septum between the foramina is made up of premaxillary bones. The incisor arches through the premaxillary in a manner similar to that in _Liomys_, with the upper wall of the root canal being formed by the upper surface of the bone. Due to the narrowness of the rostrum, the root of the incisor is prominently outlined on the side of the rostrum, both in the premaxillary and maxillary bones. With this modeling of the side of the rostrum because of the incisor root canal, and the flaring of the posterior and ventral edges of the infraorbital foramen, the side wall of the premaxillary appears as a depressed area. Anterior to the incisor root the tip of the premaxillary projects forward, and parallels its opposite, laterally, instead of turning inward as in _Liomys_. This condition, together with the prominence of the root canal, makes the anterior tip project as a flange. The premaxillary extends downward as a plate of bone, and embraces the posterior and lateral sides of the incisor as in Recent heteromyids. The interpremaxillary foramen, if present, is obscure. However, there appears to be a foramen posterior to the incisor, which possibly has taken over the function of the interpremaxillary foramen.