"Parietal breadth" is the breadth, across the braincase, taken approximately half way between the squamosal root of the zygoma and the external auditory meatus, where there is a lateral bulge in the squamosal bone.
"Mammals Obtained by Dr. Curt von Wedel from the Barrier Beach of Tamaulipas, Mexico"
E. Raymond Hall
In five of the six pairs meridionalis had a less inflated braincase, and smaller postpalatal foramina, and in each of the six pairs meridionalis had a greater depression in the frontonasal region and posteriorly more acute incisive foramina.
"Records of Harvest Mice, Reithrodontomys, from Central America, with Description of a New Subspecies from Nicaragua"
Sydney Anderson J. Knox Jones
The latter specimen is an adult male, with much inflated mastoidal bullae, nearly straight dorsal profile on the skull, relatively shallow braincase, and only slightly worn teeth.
"Comments on the Taxonomy and Geographic Distribution of Some North American Marsupials, Insectivores and Carnivores"
E. Raymond Hall Keith R. Kelson