SCIURUS 687 
section. The cheek-teeth are tubercular, brachyodont, and 
rooted. In the upper jaw, the anterior premolar (f°) is very 
small and simple, and has little functional importance; the 
other teeth (f*—m*) are subtriangular in form and have two 
low rounded tubercles (4 and 5), each supported by a slender 
root, on their outer borders; with these tubercles are more or 
less evident traces of the cusps 1, 2 and 3; on the inner side of 
each tooth is a single relatively 
lofty cusp, formed by the fusion of 
at least three elements, and sup- 
ported by a long and stout root; 
the base of this inner cusp is con- 
nected by low transverse ridges with 
the bases of the outer cusp 4 and 
5; and these transverse ridges 
form the forward and backward 
margins of a spacious and rather 
deep central valley. The lower 
cheek-teeth (f,—m;,) are quadratic Fic. 98. — CHEEK-TEETH OF 
SQUIRREL (Sciurus vulgaris). x 5. 
and four-rooted ; each has two Reproduced from Miller’s Catalogue, 
low rounded tubercles on the outer by permission of the Trustees of the 
side; a shallow basin-shaped con- Pris Museum (Nat. Hist). 
cavity occupies the greater part of the surface of the crown ; 
the inner margin of the basin is crenulate behind but anteriorly 
it rises up into a lofty terete cusp. When the teeth are fitted 
together, the prominent inner cusp of each upper molar is seen 
to work in the basin-shaped concavity of the opposing lower 
tooth like a pestle in a mortar; while the lofty antero-internal 
cusp of each lower molar shears within and between the internal 
cusps of two contiguous upper molars. As explained by 
Forsyth Major (Proc. Zool. Sec., 1893, 181), squirrels with 
cheek-teeth like those of Sczwrus may be regarded as represent- 
ing, in the molar evolution of the Sczwzzde, an intermediate 
stage, which connects the most brachyodont forms (e.g., the 
Eocene S. sfectabilis, Major, the living Rezthrosceurus of 
Borneo and Protoxerus of Africa) with the most hypsodont 
groups (the Ethiopian Xervws group, and the Oriental J/enetes 
and Rhkznosciurus). 

