1. Plate 6 (Mus musculus shown)
Old World Rats & Mice
(Mus musculus shown) B P A L
Tubercular vs. Prismatic Teeth
Plate 6
Tubercular
** In each of the following plates the upper right molariform toothrow is shown with the anterior-most tooth at the top and the last molar at the bottom of the photo. The buccal surface (adjacent
to the cheek) is to the left and the lingual surface (adjacent to the tongue) is to the right.
Prismatic cusp pattern in murids, voles and lemmings (note alternating triangles)
(Right upper molariform toothrow of Microtus ochrogaster shown)
A = anterior, P = posterior, B = buccal surface, L = lingual surface
Alternating enamel (white ridges)
and dentin (light brown material)
maintains occlusal surfaces as
the tooth wears down; enamel
is much harder than dentin
New World Rats & Mice
(Peromyscus maniculatus shown)

2. Plate 7 Inferorbital foramen Southern red-backed vole
Abrupt palate -
Transverse shelf
Inferorbital foramen
Southern red-backed vole
(Clethrionomys gapperi)
Genus Tamias
(Tamias amoenus)
Inferorbital foramen situated in the
Zygomatic plate
Plate 7
Palate sloping
downward
Meadow vole
(Microtus pennsylvanicus)
Black-tailed prairie dog
(Cynomys ludoviscianus)
Inferorbital foramen situated in projection on
maxillary bone (Tree squirrels, ground squirrels,
and prairie dogs)

3. Plate 8 Western harvest mouse Sagebrush vole (Lemmicus
curtatus) 3 lingual projections on
last upper molar a
Western harvest mouse
(Reithrodontomys megalotis)
Ventral view of upper grooved incisors
Heather vole (Phenocomys intermedius) a b
Northern red-backed vole
(Clethrionomys gapperi)
4 lingual projections on last upper molar
Plate 8
Northern bog lemming (Synaptomys borealis)
Very deep reentrant angles: (a) upper teeth cut inward from buccal surface, (b) lower teeth cut inward from lingual surface b
Reentrant angles of both upper (a) and lower (b) molariform teeth much deeper on lingual surface than on buccal surface
Prairie vole (Microtus ochrogaster) Reentrant angles of upper molariform
teeth equal on lingual and buccal
surfaces

4. Plate 9 Montane vole (Microtus montanus) Meadow vole (Microtus
Incisive foramina constrict
abruptly and narrow
posteriorly (bracket) M2
Meadow vole (Microtus
pennsylvanicus)
M2 4 closed triangles and posterior loop (arrow)
loop
Long-tailed vole (Microtus
longicaudus)
incisive foramina parallel throughout, only slighlty narrower posteriorly M3
Plate 9
M3 with 2 deep reentrant angles on
lingual side
Water vole (Microtus richardsoni) P4 M1 M3 M2
Red squirrel (Tamiasciurus
hudsonicus)
Anterior marginof orbit opposite P4
(arrow)
M3 with 3 deep reentrant angles
on lingual side; no loop on M2
Montane vole (Microtus montanus)

5. P3 P4 M1 M2 M3
Golden-mantled ground squirrel (Spermophilus lateralis)
Columbian ground squirrel (Spermophilus columbianus)
The thirteen-lined ground squirrel (S. tridecemlineatus) has similar characteristics; these two species can be separated by greatest length [GL] (SPCO > 45mm, SPTR < 45mm)
Plate 10
Higher power
Higher power
Pronounced anterior valley on P4 - M3 passes completely across the tooth (arrows)
Anterior valley on P4 - M3 does not pass completely across the tooth (arrows)
Ridge of enamel rises up
at lingual side of cusp
No ridge of enamel rises
up at lingual side of cusp