Fig. 31. Four views of the skull and a lateral view of the left lower jaw to show points between which measurements of the skull were taken. Based on M. f. primulina, from 3 mi. E Bergman, Boone County, Arkansas, obtained December 12, 1933, by B. G. Roberts; ad. ♀. 62854 Mus. Vert. Zoöl. × 1-2/5.
[EXPLANATION OF CRANIAL MEASUREMENTS]
Basilar length (of Hensel).—From the anteriormost border of the foramen magnum to a line connecting the posterior margins of the alveoli of the first upper incisors. F to F' on fig. [31].
Condylobasal length.—Least distance from a line connecting the posteriormost parts of the exoccipital condyles to a line connecting the anteriormost projections of the premaxillary bones.
Length of tooth-rows.—Least distance between a line connecting posterior borders of upper molars and a line connecting anterior faces of middle upper incisors. G to G' on fig. [31].
Breadth of rostrum.—Least distance from lateral base of hamular process of lacrimal bone to corresponding point on opposite side of skull. B to B' on fig. [31].
Interorbital breadth.—Least distance across top of skull between orbits (eye sockets). O to O' on fig. [31].
Orbitonasal length.—Distance on anterior part of skull from posterior margin of base of postorbital process of frontal bone to posteriormost part of anterior border of nasal bone on same side of skull. A to A' on fig. [31].
Mastoid breadth.—Greatest distance across mastoid bones perpendicular to long axis of skull. E to E' on fig. [31].
Zygomatic breadth.—Greatest distance across zygomatic arches of cranium perpendicular to long axis of skull. D to D' on fig. [31].
Tympanic bulla:
Length.—From posterior face to most anterior part of anterior border. H to H' on fig. [31].
Breadth.—From bottom of pit immediately posterior to external auditory meatus to medial face of bulla at right angle with longitudinal axis of skull. J to J' on fig. [31].
Depth.—Least distance from ventral face of basioccipital, excluding median ridge, to line touching ventralmost points of the two bullae. L to L' on fig. [31].
m1, Length.—Greatest length which rarely or never is alveolar length.